I can't help with pictures of MIT, but there are a few pictures of some interesting places in the Caltech steam tunnels in this essay:

http://pandora.caltech.edu/~antognini/tunnels.pdf

As a final project for a photography class a year ago, I wandered across town and took many photos of the MIT tunnels. None are online (maybe I’ll put some up someday, but since these pictures worked much better as 16"x16" prints, I’m not sure how well they’d work at a few hundred pixels on a side on a screen), unfortunately. In any case, I recommend everyone who spends any substantial amount of time in the area wander around down there sometime. It’s an interesting eerie mood (especially at 3 AM) found in few other places.

My school has 5km of (heated!) tunnels connecting all the buildings on campus, but since they're open to the public they don't feel eerie at all.

I'd like to see your pictures if you ever put them online. =)

And for CMU, a hypercard (!) stack with a map of the steam tunnels: http://www.city-net.com/~dmm/tunnels.html

Here are a few images of UCLA's underground "bridge," mentioned in the PDF above.

http://www.fortunecity.com/lavendar/hitchcock/333/

Here's an LA times article on the bridge; apparently, it used to be an above-ground bridge and then the ravine it went over was filled in and made part of the utility tunnel system: http://articles.latimes.com/2008/jul/13/local/me-then13

Wicked cool replies, thanks. =)