"The Day of the Doctor" (2013) shows that the Tower of London base contains the Black Archive housing various alien technological devices that UNIT has salvaged over the years and kept hidden away. Protected by various alien defences that erase the memories of visitors to ensure that they cannot reveal what is inside the Archive, the Archive is also 'TARDIS-proof', and has been used by UNIT as a means of assessing the Doctor's companions to confirm whether they can be trusted. UNIT is also shown to at least have access to the Under-Gallery, a secret gallery containing works of art dating back to the Elizabethan era that Elizabeth I ordered locked away as they were too dangerous for the public.