Don't know how many other people have discovered this, but you can take pretty much anything that modifies or attaches to a wall, nudge it in front of a room or make a one behind it, and use it to make a non-solid wall. The best are flat ones like temple mosaics, secret buttons, and wall text, because they can be copied and flipped around to face both directions without causing any weird bits sticking out, but you can also use wall drains, alcoves, or statues. The visible sides will stop light from illuminating the rooms behind them, but most will still have some cracks of light let through. The dungeon tileset mostly just wall text and secret buttons to create walls with, Temple is better with the mosaics and stained glass, but the best is the Prison one because it has seven different wall variations that won't stand out much. You can also use this technique to have things like ivy hang down from the ceiling:
Or also the tapestries from the temple levels. (what are for some reason called "gobelin" in the editor." One other thing is to put a floor drain over a bit, but this only works well on the Prison tileset because the other two create a conspicuous mesh clashing effect.
