The Drum was an underwater mining facility in Caithness, Scotland in 2119. (TV: Under the Lake)
It used to be the town of Краснодар, a military training site, but when a dam was broken by the Twelfth Doctor in 1980, the site was flooded and destroyed. (TV: Before the Flood)
It had a canteen, a control room, an airlock to allow them to venture outside and a Faraday cage.
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. The ghosts couldn't manifest during the day shift but could hack into the Drum's controls and switch the shift. The crew used the Faraday cage to hide and later trap the ghosts as the ghosts couldn't get through the cage doors. (TV: Under the Lake) The ghosts were released from and later retrapped in the Faraday cage, and UNIT were contacted to remove the cage and eject it into space, where the ghosts would dissipate. (TV: Before the Flood)
Crewmembers included Cass, Tim Lunn, Mason Bennett, Alice O'Donnell, Richard Pritchard and Jonathan Moran. (TV: Under the Lake)