Udvjor Gardyl
A redoubt built in the days of Baltur's hegemony, see that page for more details. It is located in the mountains of the Udvjor barony of Sormark.
Something had clearly happend here as almost nothing looked as it should and almost everything radiated all schools of magic. A huge piece of rock or something looking exactly like a gem stuck out from the entrance. Inside they found more weirdness; pillars of rock, all next to each other, perfectly hexagonal, moving up and down slowly in a sort of wave pattern.
A stone bridge spanning a vast chasm had turned to glass. When crossing it a tiny flying creature made of metal suddenly appeared; it did not speak their language, unfortunately.
Once inside the Gardyl proper, magic didn't work reliably and a huge swarm of rats, all deformed in very unsettling ways, rushed at the party. As they fled they managed to avoid some traps but in the end they all fell through a (malfunctioning?) portal.