The steam tunnels connect most if not all of the buildings on campus together, bringing steam to heat the buildings. The network is quite large, and there are many places where they should be accessible from. I have never personally been in the steam tunnels, but I have managed to research a lot about them. The steam tunnels have been a target for exploration for a long time, with mentions of students exploring going back to the 1960s, and many stories from then until now.
During the winter the signs are quite obvious, and anywhere that you can see visible steam there is probably a tunnel. The evidence can also be seen just after it snows if it is not too cold, as the heat from the tunnels will melt the snow in a straight line across the quad. I managed to capture a photo of this phenomenon, luckily. This is also mentioned in a very interesting article, linked below, where they mention the “swath of melted snow running parallel to Swift, Rosenwald, and Walker Halls is a clear indicator of the tunnel directly underneath. It makes a straight path, marking where the heat from the tunnels has melted the snow.”
Research
Here is a list of all that I have compiled with a specific emphasis on details. Many of the links have more information than I have quoted, and I encourage you to read them for yourself.
A 2007 edition of the University of Chicago magazine mentions a “network of tunnels running underneath the Midway, linking the Law School and Burton-Judson to the campus’s north side,” and that they “connect the quads to the University steam plant at 61st and Blackstone, extending west to the Hospitals and north to Pierce Hall at 55th and University.”
In the August 18th 1994 Maroon article it is stated that one of the workers walks through “a mile-long, seven-foot-high tunnel that stretches from the plant itself, at 61st Street and Blackstone Avenue, to the Administration Building.” There’s also the that in addition to the main tunnel there is are many “smaller, four-foot-by-six-foot tunnels that snake under the quadrangles to campus buildings.”
From this website we learn that tunnels run “from the steam plant at 6101 South Blackstone Avenue to a number of the university’s older buildings.” One person mentions, “sneaking into the tunnels in ’91 via a grate by the Divinity School (1025 E 58th St) … we came up in the tennis courts, only a block and a half away.”
This college confidential discussion mentions “steam tunnels from Pierce to South Campus.”
The motherload is from this Maroon article, which chronicles the story of two students. They claim that you can “get into the steam tunnels via an entrance on Woodlawn Avenue,” and that there are “two massive chambers within the tunnel system. One, they said, is at the end of the quad on University Avenue and houses a huge cluster of machines and pipes. The other, which they call “steam tunnel HQ,” lies underneath Cobb and the Administration Building. Besides acting as an access point to the tunnels under the hospitals, the area has a map on one of its walls detailing the whole tunnel system.” They also list that you could get in through a “grate (the one across 60th from Cobb was easiest.)” Also on the subjects of grates they mention that they are “all over between Pierce, the Quad, and 61st and Blackstone (the plant).”
Finally we have on of the more specific personal stories, although I will withhold their names until I get permission. Two UChicago students “crawled several hundred meters through this dirty, wet, spider-infested steam tunnel hoping that we had found an inconspicuous entrance to the main steam tunnel system from the Accelerator building basement. Turns out we didn’t: this tunnel system terminated at 57th.” The picture below was included, and it dates from around August 30, 2011, which makes it by far the most recent photo I could find.
Exploration
I finally decided to enter the tunnels on my own, although in a small way. I had noticed that certain manhole covers in the sidewalk in front of Eckhardt and Ryerson had light coming from under them, and two in particular showed a ladder. Late at night I pried one of them up and gained access to what I think is a secondary tunnel. It was quite cramped, and the bottom was sand. The tunnel appeared to extend the whole length of the quad, farther than I could see. I crawled far enough towards Ryerson to see an even smaller tunnel that probably led there, but it was too small for me to consider crawling through it.
Photos
Uchicago's Secret Places 