La Torre del Sumidero is a boat dive off Cala Blanca that centers on a lone water-collection tower standing on sand. The dive is more about an unusual man-made feature than reef structure, with an open bottom and a simple circuit around the tower. It works best as a relaxed outing from Ciutadella when wind and swell are light. Expect sand-dwelling fish, small schooling fish, and easy navigation rather than a complex route.