Auschwitz

In 1941, the Seventh Doctor cited Auschwitz to Joachim Wolff as a name on a map which would be given "new and terrible meaning" over the remainder of World War II. (PROSE: Just War)

The Ninth Doctor was present when Auschwitz was liberated at the end of the war. Samuel Preston's grandfather shot him, thinking that he was a Nazi, and locked him in a cell. The Doctor escaped and left in his TARDIS, which was in a field nearby. (PROSE: Have You Seen This Man?)