Funny you should say that, all of my newer maps make use of stairs or pathways that end in darkness to indicate doorways.
The ruins were one of my first maps and I was still getting used to map creation. I originally planned to use stairs to indicate the lower levels in the pool chamber as well, but the game engine doesn't have sideway facing stairs.
Newer maps focus on using a top down approach usually because of this.
I've edited the ruins and pool chamber to better reflect these pathways.