An invisible lift allowed transportation between Torchwood Three and the Roald Dahl Plass above. Torchwood personnel could enter or leave without arousing suspicion, since the exit benefited from the effects of a perception filter.
The invisible lift had the appearance of a slab of concrete next to the water tower. When someone stepped on it, they would become unnoticed by anyone. It could be remotely activated by Jack's vortex manipulator. (TV: Everything Changes)
The invisible lift existed as early as 26 March 2005, when it was used by Torchwood One director Yvonne Hartman to enter the hub, which was temporarily frozen by a time bubble operated by Rajesh Singh, so she could procure a Drahvin scanner from the hub unhindered. (AUDIO: One Rule)
While showing off Torchwood, Jack took the invisible lift with Gwen Cooper (who pointed out the someone could fall in the hole when the lift was being used). He used it again to stop Suzie Costello from killing Gwen, but the perception filter failed to work on her, allowing Suzie to shoot Jack. (TV: Everything Changes)