In general Iowa does not have a stellar brewing history. State wide Prohibition laws came and went, so there was a general disinclination to make major capitol investments in this area. But some of the early settled areas of northeastern Iowa had a bit of a head start, as well as some great limestone formations for lagering caves.
Highway 76 just north of McGregor was the site of the Hagensick brewery. A series of four caves was excavated circa 1867 using shovels, picks and blasting powder. They were used until the brewery closed in 1888. They were sealed in 1986 for reasons of "public safety".
Two years later the U.S. Fish and Wildlife Service, who have a station on the site, reopened one of the caves for the benefit of the local bat population. A metal grate lets the bats in and out and presumably keeps the public safe.
I don't see any bats in there. I also could not see evidence of the other three cave entrances although the cliff face has been extensively altered when the US Fish and Game folks built there. The pile of dirt and rubble in the last picture is interesting. It looks to be far too much to be fall from the roof and far too little to be remains of previous sealing attempts. Maybe it is bat guano.