Virtually inaccessible, Parque Nacional Bernardo O'Higgins remains an elusive cache of glaciers. It can be entered only by boat. From Puerto Natales, full-day excursions (CH$90,000, lunch included) to the base of Glaciar Serrano are run by Turismo 21 de Mayo.
The same outfitter also offers Glacier Serrano tours that access Torres del Paine by boat. After the glacier visit, passengers transfer to a Zodiac (a motorized raft), stop for lunch at Estancia Balmaceda and continue up Río Serrano, arriving at the southern border of the park by 5pm. The same tour can be done leaving the park but may require camping near Río Serrano to catch the Zodiac at 9am.