This came from an idea I had for a tower buried in a landslide with a stream now flowing into it, which filled it with water, eventually breaking through the cellar floor into a chasm below. The chasm can connect to another dungeon, the Underdark, or– if you’d rather keep it shorter– can just be filled with water. The tunnel in the side is a cavern or burrow whose inhabitants dug in through the wall. Or it could be from something that dug its way out. It’s meant to be flexible.
The next map will be the Great Hall of Brazenthrone. It’s going to be huge and it’s going to take a week or two. I’ll keep you posted with work-in-progress pics to let you know how it’s going.
An annotated version of this map and DM notes are available on the patreon.