Stepping through this portal is like stepping into a stained-glass kaleidoscope. Every surface is made up of arrays of brightly-colored shapes, poking out like crystals; they aren't usually sharp enough to cut, but they don't exactly make for comfortable footing, either. There's no distinction between walls and floor and ceiling; the halls and chambers rotate slowly and continuously, sometimes growing or shrinking, occasionally merging with a neighboring space or splitting into two.
Doors between rooms – those that are temporarily adjacent in the dungeon's shifting geometry – are no more than colorful sheets of glass. They don't open, but it's easy to break through them and into the next chamber. Such a chamber might be empty, or contain a victim, or be full of monsters: swarms of flying glass-shard creatures that ignore the victims, but flash to attack any would-be rescuers.
Oh, and whenever a door or any other glass is broken, there's a chance that some of its shards will glom together and turn into monsters themselves. It sure would be nice to have some way to avoid that.