About 65km (40 miles) from Puerto Varas sits Chile's oldest national park, Vicente Pérez Rosales, founded in 1926. It covers an area of 251,000 hectares (619,970 acres), incorporating the park's centerpiece, Lago Todos los Santos, Saltos de Petrohué, and three commanding volcanoes: Osorno, Tronador, and Puntiagudo. The park is open daily from December to February 8:30am to 8pm, March to November 8:30am to 6:30pm; admission to Saltos de Petrohué is $4 (£2.70) adults, $3 (£2) kids. Conaf's information center (tel. 65/486115) can be found toward the end of the road.

By far the most popular excursions here are boat rides across the crème de menthe-colored waters of Lago Todos los Santos, and there are several options. Turismo Peulla (tel. 65/236150; www.turismopeulla.cl) offers trips departing from Puerto Montt or Puerto Varas to Peulla on the far side of the lake.

From Petrohué, you can book a day trip to the Margarita island in the middle of the lake or cross to Peulla, a 1 3/4-hour crossing that departs daily at 10:30am October through April and in July; the rest of the year, the ship doesn't cross on Sundays.

Travelers may then return or continue on to Bariloche with the Argentine company Cruce de Lagos (tel. 65/236150; www.crucedelagos.cl). Andina del Sud (the owner of Turismo Peulla) has a ticket office at the pier and an office in Puerto Varas, at Del Salvador 72 (tel. 65/232811; $160-$190/£107-£127). This is a very popular and very touristy journey; though the trip to Bariloche offers rugged, panoramic views, the trip is not worth the money on stormy days. And too much of the cattle herd mentality exists here as tourist-weary guides shuttle passengers in and out quickly, over 50,000 per season. The ferry portions of this journey are broken up by short bus rides from one body of water to the other.

There are relatively few hiking trails in this national park. The shortest and most popular trail leads to the Saltos de Petrohué, located just before the lake (admission $4/£2.30). Here you'll find a wooden walkway that has been built above the start of the Río Petrohué; from here it is possible to watch the inky-green waters crash through lava channels formed after the 1850 eruption of Volcán Osorno. Apart from the one perfect photo opportunity of the crashing emerald water with the volcano in the background, there isn't really much to see here. If you're serious about backpacking, pick up a copy of the map Ruta de los Jesuitas for a description of longer trails in the park, one of which takes you as far as Lago Rupanco and Puerto Rico (the town, not the Caribbean island), where you can catch a bus to Osorno. Day hikes take visitors around the back of Volcán Osorno. One of my favorite treks here is a 1-night/2-day trek to the Termas del Callao thermal baths, the trail head of which is accessible only by boat. You can hire one of the boats at the dock (six-person maximum, $50/£33), or arrange a trip with Expediciones Petrohué, which will get you a guide and take care of gear and meals for the overnight stay. There is a rustic cabin at the hot springs; check with Expediciones before leaving for this trip to see if it is already booked. They also have rafting, 4*4 photo safaris, climbing, trekking, fly-fishing, and canyoneering opportunities. Expediciones organizes excursions for guests of the hotel and also for day visitors (Petrohué s/n, Rte. 225, Km 64, Parque Nacional; tel. 65/212045; www.petrohue.com), plus they have bike rentals.

Volcán Osorno Ski Resort (tel. 65/233445; www.volcanosorno.com) on the western slope of the volcano, with two basic chairlifts and a T-bar, is a small resort on the volcano of the same name. It has just 600 hectares (1,482 acres) of terrain, but there are sweeping views and runs apt for every level. This is not a ski resort that travelers head to Chile specifically for, such as Valle Nevado or Portillo; it's more of a novelty for those in the area during the mid-June to early October season. The snow can be armor piercing, as this side of the lake receives a lot of wind, and all the terrain is above tree level. Lift prices run $32 (£21) for a full day, $24 (£16) for a half-day, and $20 (£13) for students.

Get on the Road -- I have found that a better way than boat to travel from Puerto Varas to Bariloche is via the international highway (which is dirt is some areas), pausing for a stop at Termas de Puyehue, driving through the high Andes, dropping in through the picturesque village of Villa la Angostura, and finally circumnavigating the lake to arrive at Bariloche. Your car-rental agency can arrange the paperwork for you, or try a service such as LS Travel (tel. 65/232424; www.lstravel.com).