The Rundetaarn in Copenhagen is cool, definitely worth a visit.
I would also recommend a trip to the Science Museum in London and the Royal Observatory in Greenwich.
Also if you end up in Stockholm try and drop by the old observatory there. I went there and as soon as the attendant heard I was an amateur astronomer he got very excited and gave me a very comprehensive tour
I really wish I'd gone to Legoland, next time for sure...
