Interesting... some of your environments sound similar to my own.

Others I like are the unnatural ones: the endless bathhouse that melds into the plane of water, still waters but what lurks in the deep end... tides that wash away just a little more of your humanity with each passing. Barnacles that release acid when disturbed, kelp than binds its victims and drags them into the depths.

The forest of the dead where hanged corpses grow on trees. Every death of a blasphemer is said to grow a body, their fixed face on one of the bodies. On a full moon the trees harvest drops and hunts.

Crystal caverns, each Crystal beautiful by itself but strange. Gaze into a crystal and see yourself reflected... but older. Each new crystal you look into shows you older still. The caverns seem to echo voices, just at the edge of hearing although your own speech seems oddly muffled. The whole place is filled with hostile earth elemental and creatures of stone, except for some caverns with a pale ble tint to the crystals. The elemental seem almost scared to enter, but you don't know why.

Or the library of futures. The history of futures that never happened, hunted by the creatures that might have been. The infinite books that line these halls full of secrets and possibilities but also uncertainty - when did a history diverge? When is it not real? Is any history more real than any other, and what does it mean if you find your own life laid out there, in perfect accuracy?