Named after Fray Antonio Marchena, Marchena Island has an area of 130 km² and a maximum altitude of 343 meters.
There aren't any visitor's sites on this island, although it is possible to dive in the waters around Marchena on organised tours.
Most visitors only see it if they sail around the northern part of Isabela on the way to Tower Island, its nearest neighbor about 45 miles due west. The island's name comes from a Spanish monk, Frey Antonio de Marchena.
Like many of the Galapagos volcanos, Marchena has a caldera. Marchena's caldera is roughly elliptical and measures 7 km by 6 km, within the range of caldera sizes of the large western volcanoes. Marchena's caldera is unusual, however, in that it has been almost completely filled with young lavas, some of which has spilled over and down the sides. The oldest lavas are 500,000 years old.
Another reason why Isla Marchena is so famous is that, although it is uninhabited, it was embroiled in the ‘Floreana Mystery’. Here the dead bodies of Rudolf Lorenz and the captain of the ship he was on, washed up mysteriously on the shore of the island and were mummified naturally as there were no natural predators found here.