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At 1834m above sea level, the Eagle's Nest was built as a mountaintop retreat for Hitler, and gifted to him on his 50th birthday. It took around 3000 workers a mere two years to carve the precipitous 6km-long mountain road, cut a 124m-long tunnel and a brass-panelled lift through the rock, and build the lodge itself (now a restaurant). It can only be reached by special shuttle bus from the Kehlsteinhaus bus station.
On clear days, views from the top are breathtaking. If you're not driving, bus 838 makes the trip to the shuttle bus stop from the Berchtesgaden Hauptbahnhof every half-hour.
At the mountain station, you'll be asked to book a spot on a return bus. Allow at least two hours to get through lines, explore the lodge and the mountaintop, and perhaps have a bite to eat. Tours including the bus and guide can be booked online in advance.