Boat trips on the Beagle Channel are Ushuaia's defining experience. The channel is about 240 kilometres long and rarely more than a few kilometres wide, hemmed in by mountains on both sides — on the Argentine side, the Martial range; on the Chilean side, the Darwin Range rising to peaks above 2,000 metres. The water is deep, cold, and extraordinarily clear.
Most trips last four to six hours and cover the area east of Ushuaia toward the Chilean border. The standard route passes the sea lion colony at Isla de los Lobos, the cormorant colony on Isla de los Pájaros, and Les Eclaireurs lighthouse — the lighthouse often mistakenly called "the lighthouse at the end of the world." Longer trips continue to the Canal Murray and the Bridges Islands, where the first missionaries built their stations.
Several operators run catamarans from the Ushuaia harbour, typically departing twice daily. Prices range from around USD 40 for basic trips to USD 120 for boats that also stop at the Estancia Harberton. If you want to see penguins, check whether your trip includes a stop at Isla Martillo — not all do.