Despite Ushuaia's pretentions to the title, Isla Navarino's PUERTO WILLIAMS really is the southernmost town in the world - a tiny place lying on the Beagle Channel, and set against a dramatic backdrop of the Dientes de Navarino mountains. It owes its existence to the Chilean Navy, for which it acts as a base, but though the first things you notice on your approach are likely to be the navy's sinister black gunboats, the town is an extremely relaxed, welcoming place. The small Museo Martín Gusinde in the west of town (Tues-Fri 10am-1pm & 3-6pm, Sat & Sun 3-6pm; $2.25), has some fascinating ethnographic and seafaring relics, and is the town's only real tourist site. If you have the time, you could make the easy two-kilometre stroll east to the hamlet community of UKIKA , where you can buy reed baskets and replica canoes from families of Yámana descent (please do not intrude on family life, and ensure you respect these people's right not to be photographed). There are some excellent hikes on the island, such as the challenging five-day trek around the Dientes (or Colmillos) de Navarino, for which you'll need full outdoor gear.

The Tolkeyen catamaran   Mariana I plies between Ushuaia and Puerto Williams (mid-March to April & June to mid-Oct Tues & Sat 9.30am; mid-Oct to mid-March Tues, Thurs & Sat 9.30am; returning same days, approximately 3.30pm; crossing time 2hr 15min-3hr; $40 one way, $60 return; tel 02901/422150 or 432920). Be prepared for a rough crossing, and expect some customs delays. Return tickets are open, but if you have got an important flight to catch, remember that departures can be delayed by poor weather. Austral Broom runs a useful freight and ferry service from Puerto Williams to Punta Arenas (tel 061/218100; Nov-March weekly; $150 with bunk, $120 seat only; 32hr, but longer in high seas). For trekking information, ask at the tourist office (near the museum on Calle Ibañez) or at Turismo Sea and Ice and Mountains Adventures, which offers other interesting tours around the island. Banco de Chile, Calle Yelcho, gives cash advances on Visa and changes US dollars but not Argentine pesos. To save time, day-trippers are advised to buy their Chilean pesos in Ushuaia. For accommodation in Puerto Williams, try the excellent Refugio Coirón , Maragaño 168 (tel & fax 061/621150), which has shared rooms with bunks ($13 per person), a kitchen, and space for camping. Restaurant Camblor , Via 2 (tel & fax 061/621033) offers accommodation with private bathroom ($16 per person with good breakfast; $33 full board) and is the best option for food (huge meals for $7.50). Pensión Temuco , Piloto Pardo 224 (tel & fax 061/621113; $17.50 with breakfast) has decent rooms, and private bathrooms for a little extra, plus a $1 charge for use of the kitchen. The least expensive option is the Pensión Flor Cañuñán , Lewaia 107 (tel 061/621163; $6.50), which has rooms in a rather basic, warm hut, with the bathroom in the main house. In the evening, head to the Club de Yates Micalvi , where you can board an ex-navy supply ship and drink or snack in an intimate, sociable bar, without worrying too much if your sea legs hold up.