Vornheim / Zwillingsseen: The Temple of Icedeath

The Temple of Icedeath is a building out of pure ice. The only entrance is a big bronze gate. After knocking the door opens itself and whoever enters comes to a big hall.

For every person entering one hallway, barely high enough for the person, leads from the hall. It is so incredible cold in these hallways. Who hesitates in there will freeze to death. The hallways are around seven or eight meters long and end at a curtain.

Behind the curtains there is a shadow that will engulf anyone crossing the curtain. Whoever touches the shadow will turn unconscious and wake up in a shaft, next to a doppelganger of him- or herself.

That doppelganger is evil and wants to replace the person. Or is the person awaking the doppelganger and the other the original? The doppelganger pretends to work with it's twin though. E.g. helping them climb out of the shaft to throw them down back into the shaft while hoping to kill them.

The shaft lies a few meters behind the shadow that disappeared when merging with the character. By climbing out of the shaft, visitor can return to the curtain, hallway and main hall. The hallway is still dangerously cold.

After some time in the shaft the Highpriest of Icedeath will appear floating and try to talk to the prisoners. The Highpriest is looking for visitor to the temple whose doppelganger will show unusual characteristics. Some crank mystics proclaimed hundreds of years ago, it would have to do with the gender of the doppelganger.

Coming back out, between stalactites of ice, on the ceiling you can see a seemingly formerly not existing exit. But the ceiling is very high and the walls really slippery... The Highpriest can levitate so it is easy for him to access the quarters up there.

There is an exit from the shaft: sometimes  a small tunnel open giving visitors the opportunity to crawl out and land at the outside of the temple, near the stairs leading to the bronze gate.

On closer inspection of the main hall one mysterious extra feature can be found: the floor is actually a thick, but nearly transparent layer of ice that covers a cold, cold pool. When people end up down there, they most likely will be frozen for decades until they get out seemingly unharmed.