Catacomb map spanning a whole city
As a challenge, I decided some time ago to see if I could create a whole city map for my D&D campaign. After all, my players would spend much time and adventure there, and a complete plan would be interesting.
Then I decided that many of the city's most interesting places adventure-wise would be in its abandoned catacombs/mines (technically, they're not catacombs but rather an ossuary, but I digress).
So I made some kind of realistic plan the players would get before diving inside. Knowing strictly nothing about catacombs, I spent some time on the internet learning about them and finally found the detailed plans of the Catacombs of Paris, which were great inspiration. I then shamelessly borrowed elements from them.
I created my plan... in Microsoft Word. Just like the city map, actually. While I never finished the city map, I include it for comparison as both plans are quite related.
Note that the catacomb plans come with glorious French annotations about places, monsters and dangers.
(Edit: For some dumb reason, Word red-underlined what it interpreted as spelling mistakes before exporting, and that even though I had disabled spell-checking. Glad I switched to Photoshop Elements.)