For the first time ever I entered the Central Line at Shepherd's Bush. Just
before I went down the last set of stairs to the platform, I saw a closed
exit and what looked like a tunnel going across a set of tracks.

As I got down to the eastbound platform, I could see thru the metal grating
what looked like another platform/tunnel but about 6/ feet higher than the
platform I was on. Could see power cables etc.

Any idea what this is?

Thanks,

G