|When I run this dungeon, the entrance looks like this*.|
There is a narrow path up to the left side of the mouth
shaped cavern that leads down to the dungeon proper.
This essentially closes out the mini-Megadungeon series. It may be revisited from time to time. If my players return, I'll let you know how it evolves in my own campaign.
*Shamelessly cribbed from Google Image Search - I think it is from an episode of the Smurfs of all things.