Went on 3 week vacation to Amsterdam, Paris, Barcelona, and Ibiza last year. Going back to Ibiza next month. Had a great time in Amsterdam, but Spain was the funnest. You may not have time to make it that far south. Brussels, Belgium is not too far from Amsterdam. Ive heard good things about that place, but never visited. One word of advice- the best clubs in Amsterdam are "member clubs". In order to get in, you have to be sponsored by a member or goto with a couple good looking females who will "vouch" for you. But the clubs in Amsterdam are excellent and the Dutch chicks do dig Americans.