The extraordinary limestone sinkhole, known as Swallows’ Cave, is located near Aquismón. One of the world’s deepest pits at over 500m (over 370m freefall), it’s known for the thousands of vencejos (white-collared swifts) that nest in the caves. At dawn, flocks of swifts leave the cave, spiraling their way up to the opening. At dusk, on return to the cave, they circle above the cave mouth before they break off in groups and dive-bomb into the abyss.
It’s popular with rappelers and base jumpers who drop from the cave’s mouth. To get there, you must walk from the car park, down hundreds of steps (and back again), which is about a 20-minute walk.