The St. Cloud granite bat tunnels.  They achieved notoriety as a hibernaculum for Big Browns (Eptesicus fuscus).  In the 1950s, the bats were studied by Dr. Goehring, and in the 1980s by Dr. Mork.   Unfortunately, the spaces between the granite blocks were recently repointed (as seen here) eliminating the spaces used by the bats, so that very few can hibernate here any longer.  During one of my own visits, the only thing I encountered was a sleepy raccoon.