I think I will be able to provide you with more info here than I did for the Eastern Europe question you had.
Music - There are a lot of metal open air festivals during the summer months. In Germany they have Wacken in Wacken, Dynamo in The Netherland, Bang Your Head in Belgium, Sweden Rock Festival in Solvesborg. those are the big ones I know of that usually get 50-60 band over three days with a mix of old and new bands, and the tickets are a very reasonable $50. There are also many smaller festivals that will have 5-15 bands for one day, kind of like Ozzfest back in the USA.
Skateboarding - Your probably going to head out of the big cities to do this as the traffic and road conditions can make it quite tough, plus the streets are usualyl too crowded with people, tables, ect.
Beaches - You will find many topless beaches here. Some beaches to go to would be Valencia and San Sebastian in Spain and also some of the western coastal cities in The Netherlands.
Have you been thinking of any specific places to go? If so, let us know what and we would be able to tell you if they are a pretty good fit for you. It does sound like that you won't really have too much of a problem wherever you go.