To the northwest of the Cueva del Milodón, the Seno Ultima Esperanza continues on for about 100km until it meets the Río Serrano, which, after 36km, arrives at the Balmaceda and Serrano glaciers. A boat trip here is one of the most beautiful in the entire area. It takes seven hours and you pass a colony of cormorants and a slippery mass of sea lions. The glaciers themselves make an impressive sight, especially when a chunk of ice the size of a small house breaks off and crashes into the water. They form the southern tip of Parque Nacional Bernardo O’Higgins, the largest and least visited national park in the whole of Chile. The east of the park is almost entirely made up of the Campo de Hielo Sur (the Southern Ice Field); the west comprises fjords, islands and untouched forest.