Remains of an “outdoor museum” built by the Civilian Conservation Corps (CCC) in 1933. The concrete enclosures originally held fish, turtles, snakes, and other creatures. The museum was only open during the summer, and so captive animals were released at the end of the season.
But apparently some animals have decided to stick around! The concrete foundation still holds water, and was teeming with frogs (Lithobates clamitans) and tadpoles when I visited.