The Drum

 was an underwater mining facility in Caithness, Scotland in 2119.

Once it used to be a military training site, but when a dam broke, the site was flooded and destroyed,

Since the facility was underwater and there was no natural light, the facility was programmed to go into day and night mode to alert people on the base what time of day it was.

The base was visited by the Twelfth Doctor and Clara Oswald who arrived by orders from the TARDIS, when the base was haunted by ghosts.

Crewmembers included Cass, Lunn, Mason Bennett, Alice O'Donnell, Richard Pritchard and Jonathan Moran. (TV: Under the Lake)