The Dread Undercity: Toronto's PATH Systems

You can take inspiration from existing structures in addition to taking inspiration from spectacular wilderness. A great example to look at is found in Toronto. If every building on the surface of Toronto was left for ruin you would be left with a vast underground. Running under Toronto's financial district, and other parts of downtown, you can find the PATH. Soon to be nearly 60km of underground walkways, it is one of the world's largest underground cities. Each of these buildings alone could play host to a dungeon.



If you play on having several smaller dungeons, or levels, connected as one larger structure then you can take inspiration from a node based transit system:





Then, if you want a more orderly node structure you can rearrange the nodes in an orderly manner:



This design makes it easier to see where the lines connect and which nodes at the most important. This map is actually so structured that I am willing to bet that it could easily be run as a dungeon with minimal modifications made to the layout. It could also form the general design for an orderly megadungeon. Something like an ancient dwarven city.