The Cave of Swallows is a large vertical cave located in the Sierra de El Abra, near the town of Aquismón in San Luis Potosí, Mexico. It is known for its impressive depth of about 376 meters (1,230 feet) and a wide opening that allows sunlight to illuminate the interior. The cave is a popular destination for adventure seekers and is famous for its stunning natural beauty. This cave is also notable for its diverse ecosystem, which includes various species of birds, particularly the swallow. Each year, thousands of these birds nest in the cave, creating a spectacular sight as they fly in and out at dawn and dusk. The Cave of Swallows is a significant site for both tourism and ecological research.