This was an extremely cool experience, maybe the coolest I've ever had. I was watching from a blind near the lek with a few other birders. We were able to visit through a prairie-chicken citizen monitoring program run by the University of Wisconsin Stevens Point and the Wisconsin DNR. We got in the blind about an hour before sunrise and could only leave after every hen had left the booming grounds. In all we were in there for about 2 and a half hours. I was planning on going again this year but the monitoring was cancelled this year.
The site, Buena Vista Marsh, is a massive restored prairie, the largest east of the Mississippi. It's one of only 4 sites in Wisconsin where the species still exists, and the only one where one can reliably see birds. One of these sites has almost lost prairie-chickens, too. When watching from the blind here I also saw a Western Meadowlark, Buena Vista is one the last sites in Wisconsin for that species, as well.
A lek is pretty much the only way of seeing a prairie-chicken. I've looked for them several times during other times of the year and they are simply not seen.