Marchena Island is an 80 square miles island in Galapagos, north of Isabela Island, and it is the largest of the Galapagos northern islands. It was named after the monk Fray Antonio de Marchena, one of the first visitors on the island. Like most Galapagos islands, its origin is volcanic, with the rather unusual feature that its caldera is filled with young lava flows spilling over the sides. Although far from the volcanic hotspot in Galapagos, Marchena Island's volcano is still active, with the most recent eruption in 1991. The island cannot be visited on land, but organized tours are run here regularly in the surrounding waters for its impressive marine sites. You can visit Marchena by taking a cruise that stops at the island.

There's something to see here at any time you choose to visit the island. From June to November the waters are cooler and the Humboldt current brings more nutrients that attract a greater diversity of marine life. However, currents can sometimes be rough and the visibility limited, especially in August and September. From December to May the waters are warmer, so diving is more appealing during these months.

Marchena Island has two visitor marine points, Punta Espejo, on the southern tip of the island, and Punta Mejia, on the island's southwestern cost, that are both excellent sites for snorkeling and diving. Besides the kaleidoscope of tropical fish you can see here, you can also observe several shark species, including the Galapagos sharks and the hammerhead shark, several species of rays, like the mobula ray and the sting ray, together with eels, sea lions, sea turtles and dolphins. The coves and grottoes at Punta Mejia are a perfect place to see fur seals. The waters surrounding Marchena Island are famous for being one of the best spots where you can snorkel with schools of scalloped Hammerhead sharks.

Above the water you can spot the Galapagos hawk, brown pelicans, the Nazca and the blue-footed booby, the Galapagos petrel and the red-billed tropicbird. The Galapagos lava lizard is endemic to Marchena Island. The young lava covering the island makes the landscape rather arid, with sparse vegetation.

There's an intriguing story surrounding Marchena Island, as the bodies of two persons involved in the Floreana Mystery were found naturally mummified on the shore in 1934: Lorenz, one of the consorts of the Baroness on Floreana, and the captain of the ship he was sailing with, Nuggerod.