To get out of the tunnels at one of the labeled access points, you will need to either crawl through a very narrow space (denoted on map) or have considerable strength to lift a manhole cover. The easiest path is from the observatory to main library, but it is also in front of many people, so choose your poison. You can always exit the same way you came.

​If all you've ever done is aboveground exploring (abandoned houses, cool graffiti, secret quarries), it's time to go down under... and by that, I mean underneath Brookfield. This tunnel is close to home, free of human interference, and probably infinite (I've never been to the end). I'd recommend it for anyone who isn't claustrophobic.

The GPS coordinates of the tunnel entrance site are 43.122871, -88.114238. Park in the Kohl's Corporate Headquarters parking lot and approach the entrance shown. Follow the first tunnel and make sure to take the first ladder that you see to reach the second tunnel. From there, you can go whichever way you want - just remember how to get back to the entrance! Worst comes to worst, turn off your flashlights and follow the daylight or moonlight out.

TIP: In the image to the left (or above if you are on mobile view), the Kohl's center is tagged with a red pin and the tunnel is located on the left side of the pond (it is that gray area by the sand).

Branching off of the Menominee River, Honey Creek is enclosed partially by this underground tunnel. The entrance is marked by a large grate in McCarty Park, then winds underneath neighborhoods before emerging north of I-94. At one point, the tunnel is only 15 feet beneath the State Fair grounds! There are many turns that follow the river's offshoots, but follow the main trail and you'll rack up 2.5 miles.

Park at McCarty park and walk to the grate pictured. Depending on who visited last, you might need to unscrew the bolts connecting the grate to the wall to enter the tunnel.