Geologically this is one basin. Most geologists agree that this feature was caused by an enormous impact more than a billion years ago. The rounding of the planet as the rotation slowed is thought to be the cause of the elongation of the feature. The 61 Cygni system is full of asteroids and impacts occur with more frequency than on Earth. There was already macroscopic life on the planet, but it was exterminated around that time, leading to the dominance of the six nucleotide life.
The basin is flooded approximately every ten thousand Earth years by the waters of the Ttharmine when they spill over the Hrrst ridge. The last such episode occurred in 1731bc and is called 'The Breakout' in Kassidor's history. It was a very important event in these and the Ttharmine basins. The action of the tides during the time when the basin floor is covered is what causes the floor to be so flat.
Culturally Zhlindu and the Tduun are very different. The Zhlindu basin's culture is recent and modern. Its people are a mixture of Troll, Dwarf, Nordic and Elf. The Tduun is ancient, with history going back to the Energy Age, and racial stock derived from the Dalthites of the Borlunth basin, the same stock as the Megnors of the Lumpral basin.
The Zhlindu basin, and the city of Zhlindu are known thruout human space for heavy music and heavy drinking, and thruout Kassidor for heavy industry. It is also known for its cuisine, its laid-back lifestyle, and parts of the basin are known for magnificent scenery.
Before the Breakout the Zhlindu basin floor was an arid and hostile salt flat having very little life and almost no human life. Around the peripheries of the basin there was enough life in the hills to support scattered Troll and Nordic tribes of hunter-gatherers. The Dempalan Empire paid little attention to the area but one hovercraft expedition did explore it and eventually built a glideway line to the Tduun basin. The way stations on that line were the only human habitations on the basin floor in this era.
In 1731bc by Earth's calendar, the early 30th century by Kassidor’s, a severe quake broke thru the ridge at the present-day city of Hrrst and a vast flood was unleashed, lowering the Ttharmine sea 1700 feet and flooding the entire Zhlindu basin floor, creating a body of water who’s name we can roughly translate as 'The Sea of Reeds'. During this time Dwarves and Elves came by ship to settle the shores of this new sea. There was some warfare between the Dwarves and the Trolls and Nordics in the very early days, but the races were soon segregated with Trolls in Quanwark, Dwarves in Wescarp, Nordics in Elevnos and Elves in Kwitainia.
The sea was never deep enough to cover the volcanic plug in the middle of the basin, and people of all races began to settle the Isle of Zhlindu in the center of the basin. In a process fraught with intrigue and too complex to detail in anything short of a separate volume, a treaty was written making the Isle safe for all races, and what would eventually become the culture of the entire basin was formed.
In the hills around the sea populations expanded enormously. Cities and empires began to develop. The wizard Omiron established a large realm early in this age, ruling Elevnos and part of Wescarp. The Dwarves established many small kingdoms in Wescarp, and the ruins of the castle at Plauwlie are still preserved. That eventually became the seat of the Overking of all Wescarp, and for some time it was the greatest Dwarven nation on the planet because the Prvest basin was divided into many small states at the time, and those of Venefec remained primitive.
As the sea receded, the Zhlindu basin was one of the first to follow the Highlands into the modern age. It retains some of its unique culture and traditions, but government, aging and superstition were absent before Alexander the Great took the throne of Macedonia.
This basin, and especially the isle or city of Zhlindu, is now a melting pot of the four major races on Kassidor. The culture that has grown there owes a lot to all those races, with the Elves bringing technology and learning, the Dwarves bringing their love of a good time, the Trolls their strength and close-knit communities, the Nordics their love of adventure. When it was all blended together under the influence of genetic changes from the Kassikan, a unique culture evolved, devoted to good times, good music and good friends. In it the Elves gave up their ambition, the Trolls gave up their xenophobia, the Dwarves gave up their hierarchies and the Nordics gave up their strict moral codes. Today only a third of the population identifies with any one race, and racial discord is virtually non-existent. All participate in the same culture, but it is a culture that allows for lots of individuality, even by Kassidorian standards.
The economy itself is rather primitive and the Zhlindu basin is not very affluent by Kassidorian standards, but the level of creature comforts are more like the Highlands than the Kyeb basin. The city of Zhlindu has little natural energy resources, so much of its great industries are driven by cordwood and muscle power. Keda-drawn streetcars are common and cheap, but most commerce moves on sailing ships crewed by amateurs who tend sail in exchange for passage. The population would rather play than amass a fortune and hardly anyone works for more than they need.
Sexuality is more easygoing than in the Highlands. The body as art is not as rampant, but still people are attractive and healthy. There is less pair bonding than in the Highlands, but sixty percent of the population shares a home with a long-term partner. The climate on the basin floor is pleasant when 61 Cygni is quiescent, but becomes quite stifling during periods of high activity. Women don't wear tops during daylight, going out on the town in the nude is not uncommon, but the public flaunting of aroused genitalia is not common except in clubs dedicated to it, which are not very common.
People in the Zhlndu basin are more likely than others to spend some part of their life in the country and some in the city. Fully 70% of the population has lived in a city long enough to buy a home but at any one time, only 18% of the basin's population is living on property that doesn’t grow enough to feed them.
There is a large tourist trade in many parts of the basin. Wescarp and Quanwark are known for spectacular mountain scenery. The city of Zhlindu draws long-term tourists from all parts of the basin, primarily for the music and the drink, but it is a spectacular scene in itself and one of the cultural hot spots of the planet.
Quanwark has the steepest, tallest mountains, more rugged than the spine of Centorin. If you intend to go beyond the villages, pick up a good crossbow and learn the rudiments of shooting it while you're in the town where you dock, purchasing a weapon in a country village may require strong social connections in Quanwark. Once you are out of the small cities along the Imoneeya, the lower slopes are cloaked in dense shaftwood forests full of old-style cut-log Troll villages. You will see ax-throwing competitions and drink hearty stouts in them. Troll women are beautiful now, with thick dark curls and impressive figures. Above the forest, alpine peaks abound with scamps and coriscamps. (A coriscamp can be trouble if you're unarmed, they're much faster than they look.) But beyond the upland meadows lie some of the most spectacular climbs in human space. You can find anything from a steep ascent to a mile-high wall of bare rock. The peaks of the Quanwark range are above 45,000 feet barometric, but you can get five miles above the basin floor with no more gear than a decent pair of sneakers and a water pack. The view is almost like a view from space but you are at the barometric altitude of a downtown street corner in Kex.
Wescarp has the prettiest mountains. Most tourists from Zhlindu go to inns in the Central Wescarp Range, with the biggest along the Hazorpean-Noonitondow coach road. You can get coaches all over Wescarp. Unlike Quanwark, the rollicking Dwarves of Wescarp cater to tourists and there are music halls in little bitty hill towns so small that you couldn't even find them if you wandered off the road. There are challenging climbs in Wescarp, the Kendaids are both challenging and scenic, and the view of the Central Wescarp Range across the Central Wescarp Valley is more interesting than the view of the flat basin floor. Those who would like to see the view without the challenge can hire coaches to the tops of several peaks in the Central Wescarp Range, the highest is eleven thousand feet above the basin floor, the basin floor is on one side, the Central Wescarp Valley on the other. If you go into the wilds of Wescarp, pick up a crossbow and learn how to use it. Unlike Quanwark, the armsman will be courteous and knowledgeable and probably treat you to a round of cups if you’re sleeping in town before you use it. Out in the wilds, just a big nyobba can give you a nasty bite and some have the disposition to bite first and ask questions later. Those hide from the hyadunes, hakken packs and the occasional theirops that hunt the plentiful herbivores in this forest. Lenta are excellent eating and any cook at the town you slept in last will pay more for the field-dressed animal that he'll charge you for all you can eat of it, side dishes included.
Elevnos has pretty hills of farms and woods. It is known for busty blonds, though all races are found there today. The public houses are not quite as tourist friendly as Wescarp, but that does not mean you and your buddy will sit alone. There is scheduled coach service in Elevnos but it is only on the main roads to towns of fifteen to forty five thousand in size. Outside the towns, the countryside is really pretty with overgrown paths all shaded with produce blooms, stick fences woven with vines, rough stone bridges, long, low porches on the fronts of the houses with ornate vine rails. However, many visitors to Elevnos miss all that because of the nude women bending over their gardens. The wilds of Elevnos have less dangerous wildlife than Wescarp, but it would still be a good idea to be armed if you’re walking lonely paths. There are a few wild karga, and like Wescarp, any cook will pay more than you can eat, but don't come all this way just to hunt karga.
The basin floor is mathematically flat, but the inhabited parts are made pretty by the inhabitants. Fences and houses are covered with flowers (much of them larorlie). Homes are nicely decorated with laced vinework and fine woodwork and fields are small, well-tended and lush. The natives of this area are descended from those of the countryside around it, and along the slice of the basin drained by the Lhar they have come largely from Wescarp. Thruout the basin floor you'll find coaches, public houses, friendly taps and good live music in villages that would have nothing but a dented old kiosk and a graffiti-covered public station on Centorin. Anyplace on the basin floor is as good as anyplace else. You could spend a lifetime seeing different details of the basin floor, the tiny dots with names on this map are cities of millions that it takes all day on a coach to get out of. They each have competing, city-wide slick magazines about the concert scenes in the big halls in their centers.
The wilds of the basin floor are mainly prairie teeming with large animals. Huge herds of thongaa and blanth abound. At first glance it is a hunter's paradise. It certainly is. Theirops and several of their relatives are an ever-present threat and the largest carnivore known to man, the kranjan, thrives there. Do not go deep into the wilds of the basin floor without a well-armed guide and don't make a kill late in the light. This is important. You and a friend can pick up fine crossbows at any town on the way and bring down more meat than you can carry just a few hours out. Most other hunters will stay away from you while its light, but to be sitting and enjoying a nice sunset, with the field-dressed meat already hanging, as the forty hours of darkness descends across the plain would be a very bad idea. For instance, hyadune climb trees better than a squirrel. There are estimated to be about 35,000 theirops out there somewhere on the basin floor. Hakkens hunt in packs. If both you and your buddy empty your quivers of arrows into a kranjan, it has just enough nervous system to feel that and will probably find it annoying enough to come after you.
The people of the Tduun are called Tundrites by the remainder of the planet, because they have the same look as the Tundrites of the north. Gene-spread says they came from the Borlunth basin during the Energy Age, and that they are a branch of the Dalthites that occupied the Borlunth basin before the Trolls drove them out.
They call themselves Tduun or even Dalthite. The men are slighter built than the Megnors of the Lumpral basin and their skin is not as paper white. Most have shiny black hair but some have brown or even dark orange, occasionally almost white. The women are not usually as small as the Megnors of the Lumpral basin, but even so, many are called Pixies if they come up into the Zhlindu basin.
When out of the basin they are sociable to all, but outsiders don't generally find a warm welcome in the Tduun even now. They will conduct business but you will not find many opportunities for socializing and sexual encounters in the basin itself, especially outside the city of Gorunda.
Among themselves they are quite social and the women still follow the Megnor tradition of taking great delight in their breasts. The culture has changed relatively little in the modern age, even less than the deeps of Lumpral. There are still village chiefs with harems, there are still important ceremonies for birth, death and marriage. Incest is still common and accepted, especially between fathers and daughters, and some families will have elaborate ceremonies when a father takes his daughter’s virginity.
The village chiefs have no coercive power, of course, but the social pressure to follow the chief's dictates can be severe enough to cause people to leave the area. In the cities there is none of that, and the urban people often act close enough to the Kassidorian norm to fool you. In the cities many of the women are independent minded and educated and it sometimes happens that they will accept an encounter with someone not of their race. However, if you're looking for an encounter with a Pixie, you're more likely to find it in Zhlindu. Most of the Tduun who want to participate in the modern culture 'go up to the floor' as they call it, and leave the Tduun and its ways behind.
With all that said, the Tduun is very mainstream compared to the conditions in the Tthmurng basin where life continues as it has since before the Energy Age.
Like all peoples derived from the Fmak, their notions of music are not compatible with most of the remainder of the planet and the remainder of the human race for that matter. It is reedy and arrhythmic and seldom used for entertainment. It is associated with ceremonies and traditions. Some people do have sound systems and import music from the Zhlindu basin in the cities, but it is not common in the countryside.
Most of the Tduun seas are now covered with wildhull swamp and the Kassikan will not allow enough weaponry onto the planet to allow even a large force to travel that area safely. Do not enter that area under any condition unless you want to know what it feels like to be consumed by a large predator. There are dactyls above, numerous megamillitentacloids, spheelunge and spiker bushes below, hyadune and droppers in the trees, poisonous worts and rots and even the occasional swamp swallower to take you, boat and all.
About the only reason for someone to visit the Tduun is to get to the Tduun pass and the Trastrab, Prvest, Borlunth and Trenst basins beyond. To do that, sail from Gorunda to the Tduun pass and make sure you stay well south along the Troll coast and well away from the wildhull swamp.
When the Tduun was settled, the remainder of the Zhlindu basin was salt-flat, desert and scrub. The Tduun was fertile and the Sheeldoreks were more fertile than Elevnos at the time. The area was settled during the Energy Age, with the oldest sites dated to 3088bc. There were no Tduun and North Tduun seas in that age, just rivers that ran to sinks along the Tduunzhorp.
For five hundred Earth years during the Energy Age, the Tduun was the only area served by the glideways in the Zhlindu basin. It was nominally under the control of Dempala but highly autonomous. The Dalthites of the Borlunth basin had resisted Dempala for many decades until the Elves armed the Trolls of the Fronzhorps to aide them. That lead to the extermination of the Dalthites in the Borlunth basin and their diaspora to the Trenst, Knidola and Tduun basins. The Tduun had been totally uninhabited till then. It is impossible that these people could have crossed the Tduun pass without breathing apparatus, at the time they could not survive air thinner than that found three miles below Earth’s sea level. It is not known if they stole Dempalan equipment to make the crossing, or if they were aided by the Elves. In its early days the empire was not bloodthirsty enough to commit genocide.
The Fall did not affect the Tduun basin at all, except that the chieftains became completely sovereign instead of nearly so. There were five kingdoms thru most of the Troubled Times and in their isolation they regained and even surpassed Dalthite culture. For seven hundred years they were one of the most advanced cultures on the planet.
In the Troubled Times there was a rigid class distinction with the lowest class males barred from reproduction. The aristocrats lived in large and ornate palaces with rooms full of servants and fields full of serfs. All attractive women were taken into the harems of the aristocracy where they lived in luxury and splendor. For the aristocracy there was learning, literature, fine carriages, lavish clothing and glittering social events. This was supported by vast plantations of slaves, a part of their history that the Tduun of today tend to downplay.
As a first order approximation, the history of the Tduun basin ended with the breakout. All the great kingdoms were drowned under a relentless cascade of rising water. Most of the population lost their lives because most fled to the Sheeldoreks instead of the difficult slopes of the Tduunzhorps. The waters continued to rise until the all the Sheeldoreks were submerged.
Half the land that the great Tduun states occupied is still under water. Most of the survivors were in the Tdunnzhorps and it is their descendants that have re-populated the basin and exhumed the relics of their vanished past. For the Tduun basin and the Tundrite people, the breakout was The Flood. Before the waters receded enough for them to regain their former glory, the modern age was upon them and they have been out of the mainstream ever since.