Cerro Tronador is the standout attraction among many day-trip and hiking options in Bariloche. It is named for the thunderous sound the volcano made before it went extinct, but the name (Thundering Mountain) is still apt, for the rumbling icefalls as giant pieces of ice shed from the glacier, which are audible at a safe distance. The main attraction is the Ventisquero Negro (also called El Manso), which means black glacier, and it’s easy to see why. It is mainly covered in darkish soil and moraine, and small pieces that have broken off float in a milky lake at its foot.
The glacier is the source of one of the nearby rivers, called Río Manso (tame river), which you can also see, and there are waterfalls, including the impressive Garganta del Diablo (Devil’s Throat), where several waterfalls come together.
Cerro Tronador looms over the hamlet of Pampa Linda, you arrive at after driving along U-shaped, pale blue Mascardi lake. Visitors can hike up to the glacier at Refugio Otto Meiling (where you can also spend the night) and keep going until the road ends at the Garganta del Diablo falls. You can also do this part by bike. In either case, you’ll want to be careful not to get too close to the falls’ edge.
The gravel road out of Bariloche does one-way service to Cerro Tronador in the morning, and back in the afternoons, and it is slow going, as it is unsealed (ripio). The drive can take two hours or more, but unpaved roads are what crisscross most of the region, including the Ruta 40 which runs down the spine of Argentina’s part of Patagonia, so this is fairly typical outside of the well-touristed part of this region. You’ll have to rent a car or do a tour to visit the Cerro, as there is no public transportation.