Who knew Batman’s summer home was in the center of Phoenix? Though the tall masked vigilante will remain elusive, this flood control tunnel offers an incredible (and free!) opportunity to view thousands of Mexican Free-Tailed bats.

Every year from May to October approximately 10,000 to 20,000 bats flock to Phoenix on their migration south to Mexico. During the day, they gather within the “cave” to rest and sleep. But at night, they emerge and fill the sky.

The bats start to leave the storm drain just before dusk and continue into the night. It’s incredible to watch them whirl through the air, flapping around while they dive after insects. Stand quietly, and you can listen to them squeak and chirp as they embark upon their hunt. They don’t seem to be afraid of people, so don’t be surprised is they zoom right by you, mere inches away.

The bat cave is a hidden gem within Phoenix. It can be hard to find, making this chance to witness so many bats at once a special treat for those who are in the know. There are a few signs from the Arizona Game and Fish Department around the area to educate the public on these creatures and encourage quiet viewing behavior.