the opposite of walls

I haven't used dungeon tiles in years, but I sometimes like to relax by watching people make their own tiles. I'm talking about folks like DM Scotty, Wyloch, Black Magic Craft, The Tabletop Engineer, Professor Dungeon Master*, and DungeonMasterG. There's just something soothing about watching someone turn a bit of corrugated cardboard or some foamcore into a little piece of dungeon architecture. I especially like the painting, where often simple mixes of blacks and whites and greys become a sophisticated dungeony look.

But something has bugged me about dungeon tiles for a long time. They tend to encourage two-dimensional thinking. Sure, we have 3-D figures, and maybe furniture, too. But they all exist in what tends to be a flat plane. And I think the presence of walls on tiles, although aesthetically pleasing, doesn't do much to help in getting the DM and the players to think in three dimensions. Crooked Staff Terrain recently has done some work to alleviate this problem, but today I want to talk about the problem with walls specifically.

I'm going to start with a very simple argument: walls are so ubiquitous in dungeons that, in most circumstances, you don't need them on the playing board. For example, I tell you that the corridor you're going down ends in a T-intersection. I then put down this tile:

 You have a pretty clear idea of where the walls are and where they aren't, don't you? If there is ambiguity, like say the western leg of the T turn's north, then an additional 10'x10' tile should do the trick:

(I've gone to 3 squares for a 10' wide tile because I think that better fits. 2 square wide corridors always seemed super-cramped to me. And Gygax recommends 3 and a third foot squares on page 10 of the first edition DMG. As I recall, Empire of the Petal Throne allows 3 adventurers breast in 10' corridors as well. There's more variability there, though. In EPT you can fit 4 abreast if no one is wearing metal armor, while 2-handed weapon users can only fit 2 abreast. Except for 2-handed sword wielders, who need the entirety of the 10' corridor to operate properly.)

Below is a normal corridor. What if I want to represent that one side of it has no wall, but rather looks down on something below? Since dungeon delves involve piercing deeper and deeper underground, I think that would be a more common scenario than the stacking up that Crooked Staff does in the video I linked above.

Here's one idea how to represent that:

The black part represents the yawning void where the east wall should be. There's got to be other ways of depicting this sort of thing, so that adventurers can better interact with the 3-D dungeon environment. How do I show, for example, that there's more dungeon down there?

(BTW, these tile images were made with the Flagstones font. S. John Ross made it many years ago. It's a pretty great way to crank out a lot of paper tiles quickly. I don't see it currently listed at his store on drivethru, but he has lots of other cool stuff there for sale.)

*Special recognition for Professor Dungeon Master who, in addition to great crafting videos, has some really sound DM advice videos.