South Kensington station is not a 'disused' underground station. A visit pre-arranged by LU was to see the disused parts of the station.
Info from the abandoned stations website:
The District Line obtained powers to build a deep level line along the route of its existing line to relieve overcrowding (the deep level line would have been an 'express' line i.e. would have had less stations). Construction work was actually started but was halted after it became apparent that the opening of the new Piccadilly Line was providing adequate alternate relief. A station and tunnel had been built at South Kensington - it was used for subterranean offices and a signal school until the station was remodelled for the installation of escalators.
Most of the deep level District section is lost now, its space taken by the escalators and associated passageways to the Piccadilly line platforms
