Lago Nahuel Huapi's entire Quetrihue Peninsula, with its unique forest of arrayanes (myrtle trees), is protected by the Parque Nacional los Arrayanes. These trees absorb so much water through their thin skins that all other vegetation around them dies, leaving a barren forest of peeling cinnamon-color trunks. A stroll up and down wide wooden steps and walkways is a memorable experience, as light filters through the twisted naked trunks, reflecting a weird red glow.
You can make this excursion from the pier at Bahía Brava in Villa La Angostura (or by boat from Bariloche via Isla Victoria). In summer, you can walk (three hours) or cycle, after registering at the Guardaparque office (ranger station) near the pier. Leave in the morning, as the park entrance closes at 2 pm. A nice combination is to go by boat and return by bike (it's all downhill that way). If returning by boat, buy your return ticket at the pier before you leave.