Probably wouldn't want to be there today. ;) (Lots of rain, I think the tunnels are full.)

A couple years ago we stopped by the Lincoln Oasis (rest stop consisting of a bridge over the interstate that carried restaurants and similar instead of traffic.) As I was heading back to my car, I heard a loud whooshing noise and saw what looked like a geyser next to the ramp to get back on to the highway. I walked over to inspect and found a large grate fenced off and signed Chicago Water Reclamation (or something similar.) We had had a lot of rain the night before and apparently this was a vent to release air as the tunnel filled. The location is very near one of the quarries that is used to hold excess runoff.