Can anyone think of some good London riddles?

We're hoping that you guys can help us out and think up some good London riddles. We are doing a Treasure Hunt around London (just an online one, not a real world one - http://www.londondrum.com/quiz/treasure-hunt.php) and need to dream up some clues.

As an example, here is our opening one (which is very very easy)

Stick a needle in your eye,
it doesn't fit... I wonder why?

The answer to that is Cleopatra's Needle, but that was easy. And here is one that is a bit better:

I stand upon my lofty seat,
to warn the people in the street:
"Beware the lions at my feet!"

Maybe you can work that one out.

But we need millions and bazillions more. Can anyone think of some good ones? As long as they refer to famous locations in London they will be great. They can be anything from popular tourist attractions to famous streets and historical sites -- as long as its a famous place in London.

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