Some ideas of what to do in London with teens?

[schoolgaterebel]

We have a day in London with our teenagers coming up and I was wondering if anyone had some ideas of things to do?

They are interested in most things, and also love food and trying new cuisines.

Cheaper or free activities would've great as we already have a 'spendy' trip planned this summer.

The art of the brick exhibit on south bank. Not cheap though!
Camden
Covent Garden
Brick Lane
Greenwich - go on Thames clipper from Embankment (check the market is on)

See the Harry Potter sights in London?

Bowling at brick lane. Don't eat there, more expensive. A curry or street food?

Or bagels on brick lane, actually!

Thank you for some great suggestions so far...looks like we may need more than one day!