Power room
From Tardis Wiki, the free Doctor Who reference
The power room was a part of the TARDIS to which the Second Doctor once retreated immediately after using the emergency unit. Located just off the console room, it was key to fixing the TARDIS after the ship popped out of reality. Presumably, the power room was at least the location of something having to do with the fluid links, since the failure of this part of the TARDIS necessitated the use of the emergency unit.
Both Jamie and Zoe spent some time inside the room talking to the Doctor. (DW: The Mind Robber)
Behind the scenes
It's never revealed in the serial exactly what the power room does.
