The Haus der Berge is the visitor centre for Berchtesgaden National Park, a modern building in the town centre with a permanent exhibition on the park's ecosystems, geology, and wildlife. Entry is free, which makes it an easy addition to any day. The displays cover the full vertical range of the national park's habitats — from the lakeshores of the Königssee to the high alpine zone above 2,000 metres — and explain the distribution of the park's notable species: golden eagles, chamois, red deer, and the rare Apollo butterfly.
The centre also has good hiking maps and trail information. The national park itself is Germany's only Alpine national park and covers 210 sq km of mountain terrain. The visitor centre is the best starting point for understanding what you're looking at when you take the boat down the Königssee.