Thirteenth biggest island of the Galapagos, Tower covers 5.4 square miles. It is relatively flat reaching only 250 feet (Compare with Rabida, 1.9 square miles and 1,203 feet.) The volcanic origin are evident from its outline. What today is Darwin Bay was at one time the caldera of a volcano. After the volcano became extinct, wave erosion wore away at the walls and eventually broke through forming the bay. It is also called Genovesa, after the place where Colombus was born Genoa, Italy. However, the English name is more widely used. The origin of this name is not certain, but the circular cliffs surrounding the main bay are reminiscent of an ancient fortress. It is the most remote of the islands with land Visitor Sites and most visitors do not make it here. However, those that make the long sea trip, an overnight voyage, are richly rewarded. Huge colonies of various seabirds, provide a spectacle unparalleled elsewhere in the islands or perhaps the world. The birds make such an impression that one cannot fail to be astonished. Especially numerous are the red-footed boobies which make up the world's biggest colony of this species. Brian Nelson, a British researcher who studied the boobies on Tower was so impressed that he titled his book Island of Birds. Other birds here include masked booby, frigatebirds, Galapagos dove and Galapagos owl. Two species of storm petrels have a vast colony on the eastern side of the island, totalling over 200,000 pairs. In recent years pairs of waved albatross, that normally breeds only on Hood Island, have been observed courting near the petrel colony, although they have not yet established successfully.