Hostel

What are you interests?

London offers so much to see and do - if you are more specific with your interests, you will no doubt get some good recommendations.

ps Factor in the weather for any outside interests.

The British Museum is fantastic and free to enter. Particularly helpful if it is raining when you are in London. website

how much is the hostel for one envening and what is the address please?

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<hr>Madame Trusseaus?<hr></blockquote>
Madame Tussards - but it's probably at number 999998 in things to do in London

Third time lucky - Tussauds

You can't visit london without going to the Tate Modern Museum ... A wonderful place for everyone like modern art (Free, like others museum in london)
I think you have to go also to the Camden Market, an incredible market as a labyrinth in old warehouses in the north of the city (Also free if you succeed to buy nothing).
Have a good trip,
Mathieu.

NESST

Another vote for the British Museum or the Science Museum if it is raining. If Art is your thing wander around the art gallery but as others have said you need to be specific.

Covent Garden is always good for street entertainment (free if you disappear when the hat comes round!), and is central (v close to Trafalgar Square).