When the weather begins to warm the evening, bats flood the night sky. And while the spring and summer are some of the best times to see these animals in flight across the United States, bats of various shapes, sizes, and species stake claim to caves, bridges, and other locations as their homes across the globe no matter the time of the year. These colonies are vital to the ecosystems they populate and many are environmentally protected locations. 

The largest urban bat colony in North America resides under the Congress Avenue Bridge in Austin, Texas. The bridge is home to around 1.5 million Mexican free-tail bats. As the weather gets warmer, the colony becomes more present. Deep underground in Beer, England, is a quarry that dates back to Ancient Rome. Quarrying ceased during the 20th century when the cave became a site of special scientific interest. Today it’s the home for hibernating natterers, whiskered, and several other bat species.

From an abandoned mansion now housing an endangered species of bats to a railway tunnel turned microcolony, here are 21 of our favorite bat haunts.