Terezin (Theresienstadt in German) was a small concentration camp, more of a transit camp, outside of Prague during WWII. It was "home" to thousands of Jews and political prisoners until liberated by the Red Army in May 1945. The Jews were kept in a ghetto until they could be transported to death camps like Auschwitz. Nearby is the Small Fortress, which had been used on and off as a prison for a few centuries, most recently as the prison for the assassins of Archduke Ferdinand.
The Small Fortress is now a memorial; the National Cemetery is on the front grounds.