In January 1942 a group of 15 high-ranking Nazi officials met in a stately villa near Lake Wannsee to hammer out details of the ‘Final Solution’, the systematic deportation and murder of European Jews. The 13-room exhibit (in German and English) in the very rooms where discussions took place illustrates the sinister meeting; it also examines the racial policies and persecution leading up to it and such issues as how aware ordinary Germans were of the genocidal actions.
You can study the actual minutes of the meeting (taken by Adolf Eichmann) and look at photographs of those involved, many of whom lived to a ripe old age. The site is about 2.5km northwest of Wannsee S-Bahn station and served from there by bus 114 several times hourly.