Time Vault Zero

Time Vault Zero was the deepest of the Time Vaults on Gallifrey. It contained the Moment, a forbidden weapon which was locked up here for billions of years. (PROSE: The Day of the Doctor)

Rassilon locked the Moment away in the Omega Arsenal after he deployed it against the Nestenes. (PROSE: Pandoric's Box) Its "final" resting place, Time Vault Zero, was considered impenetrable. The contents of this vault were an open secret among Time Lords. (PROSE: The Day of the Doctor)

On the final day of the Last Great Time War, the War Doctor recovered the Moment from the Time Vaults, and brought it with him into the Drylands, planning to activate it and end the Time War once and for all, killing Time Lords and Daleks alike. (TV: The Day of the Doctor) The General's troops were alerted, but were unable to prevent the Doctor from entering the time vault and stealing the Moment. (PROSE: The Day of the Doctor)