In the middle of the serene Eifel National Park looms a hulking modern castle with a dark history. Ordensburg Vogelsang was built by the Nazis as a party elite leadership training college and is one of the largest remaining Third Reich buildings. In 2006 it was developed into an international centre of tolerance and peace. The spanking new visitors centre has two excellent exhibits on the compound's Nazi-era period and on the natural history of the Eifel National Park.
After WWII Vogelsang was used as a military training site by the Belgian army. You're free to explore the grounds on your own or to join a guided tour (in German). Don't miss climbing up the tower to take in the immense size of the complex and how it fits into the idyllic surrounds.
To get there by public transport, take a train to Kall or Simmerath, which will be met by the Eifel National Park shuttle SB62 or SB63, respectively. Both go straight to Vogelsang. See www.vrsinfo.de for timings.