I am flying First on Qantas to London soon and will have a couple of hours to kill at Heathrow between flights. Just wondering if people can help with things for me to do:

1. Where is the best spot to view aircraft movements?
2. Is the Moulton Brown Spa worthwhile? What "treatment" should I get?
3. Which is the best lounge? Do they still have a "Concorde" lougne? Can I use it?
4. Is it possible to leave the terminal building and have a look around?
5. Anything else?

Thanks