Camlann Hill

The place of King Arthur’s end, which was caused by the betrayal of Round Table knight Mordred. Unlike other Servants who are summoned to the Throne of Heroes after death, Saber became a Heroic Spirit while still alive, using her soul after death as collateral. Until she is able to obtain the Holy Grail, she will perpetually return to this moment right before her death.

Fate/Zero Animation Guide II: Glossary of the holy grail war II