Dreamt of a large group of people who constructed a portal, but ******** up.
They found themselves in a world of glowing crystal. Not an ounce of soil to be seen, a singular near ice cold river disturbing in its consistency, a group of barely sentient, tiny mushroom people.
There was no sun nor moon. The land was illuminated by its own glow, dim yet constant. From the sky, which seemed to be a distant mirror, a single beam of light broke out, which they determined to be the connecting point to their homeworld.
They had assumed it would be a simple task to get home. All that was necessary was an altar made of the same material they used to create the one that sent them here.
They made it out of limestone.
There was no normal stone in sight.


So, they decided to make the best of what they got, and attempted to find a way to survive in the strange land. Mining in the traditional sense didn't work, the crystal was neigh impenetrable, but they found that bringing ice to it caused it to fall apart as if sand. With ice, it was absurdly easy to manipulate, and the crystals themselves seemed to welcome movement.
Within a year they had crafted a spire that rose to meet the source of the light, the hole in the mirror, yet they could go no higher. It was magic that sent them, and it would be magic that returned them. So they crafted, atop the tower, a garden of water with a pedistal in the center, prepared to one day house the altar they'd use to return.

Food quickly turned out to be simple to acquire. For the first week or so, they managed to trade with the native mushrooms for supplies, but quickly found that edible plant like structures grew on the underside of the crystals. Three days in they had started mining, and on the fifth this strange entity had grown to completely cover the tunnels they were clearing out.
Mining itself was also far too simple a task. The crystal seemed to float, and it never caved in. The manmade caves were naturally lit, and so long as you had access to some form of ice you could bend them to your will. And there was never a shortage of food.

In one direction, which they arbitrarily labeled north, there was a land of green rock. It was much unlike the crystal they had found, and was completely barren of life. They found it by following the river in both directions, which lead out of and into these lands. Within, the rules changed.
Water began to flow uphill. Light was drawn into the rocks, which were barely visible even when lit by the brightest of crystals. Life disappeared. And the only protection from the ailment was a sufficient amount of ice on your person.

Yet more industrious, the people set about building a wall around where they had settled. Using the green rock they managed to force the river to go over the wall. They also built two more monolithic towers.
Atop the first, they cast a spell of blinding light, projecting onto the mirror in the sky a gigantic radiant orb that mimicked the sun. Atop the second, they crafted a lesser spell of light that projected a less brilliant orb to mimic the moon. Each of the three towers were placed equal distances apart, near the wall, creating a large triangle. And after their construction was finished, the people found something anew.
Within the triangle, the crystal would remain suspended midair. They couldn't say why, but with it they crafted a floating city within the walls, extending miles into the air.


As for less crucial things, they clothed themselves in crystal mail, as in small rings woven together. It doubled as armor, which generally proved to be unimportant.
And they slept on beds made of crystal dust. A lack of readily available cloth meant that they could only really use chains, and as there was very little flammable material around they utilized the lighting of the crystals instead. The landscape was naturally warm in most areas, so for the most part the very idea of heat was forgotten about.