Spending a week in England (3 nights in london), a week in Rome, a week in Amsterdam and a week in Barcelona.

I've been to London, Rome and Barcelona before, but it was awhile ago and I can't remember much.

Any tips from the anyone here on things to do/see etc in any of these cities?

In Amsterdam, go to the redlight district, find a weed bar, then hunt down Joran Vanderslut and show him some outback justice.