Where am I supposed to go in these tunnels?

There are two subway wrecks along the very outside ring.  Check those out.

All the important rooms have been shaded, and will be marked with a "?"
until you've been inside.  Try each of those out.

In the upper-left quarter (where you enter), you should find a "machine
room" and pick up an eel sculpture and a robot part.

In the lower left, you should find the "lava room" and "crab room".

In the lower right, look for the "sentry room".