Far northwest of the Galapagos archipelago, about 150km (90 miles) from the main port of Puerto Ayora, we find Tower Island (Genovesa in Spanish). The southwestern part of the island is formed from a submerged caldera, partially opened and flooded. There is a deep part of this caldera located right at the center where large manta rays and hammerheads are frequent visitors. These fish sometimes swim close to the more open western edge of the caldera. Tower Island offers two very distinct snorkeling spots along the cliffs that form the inner part of the caldera. Snorkeling here is great as you gaze down into the depths to spot large fish.