@Ray7: Yes, but you have to be security vetted beforehand, and there are only a few places you can go (mainly departmental displays in the main concourse, and a guided (or 'overseen' as it may be) tour of the basement server rooms.
That's a shame ...
I used to be security-cleared, but that was years ago.
When I was there they were doing a lot of work on reducing power consumption; the bit I remember was that a Second Life avatar used more electricity than the average African
Ian2 would be pleased to know that there is also an internal road/race-track within the building itself -- presumably so they can race when it's raining.