Well, if we can narrow from countries down to cities I can offer some suggestions. I recommend getting the Spartacus travel book from your local gay bookstore or order it from Amazon.
Amsterdam is a very gay friendly city with lots of options no matter what you're into. Also, it's beautiful and most people speak English. Gorgeous looking people too.
Berlin is absolutely wild with parties every night. The scene there is pretty full on and it leans to a slightly more hard core gay scene.
London is the NY of Europe with lots of gay options. Very expensive city though.
Paris has a very active gay scene as well, not to mention, another gorgeous city. Lots to do.
Barcelona is the San Francisco of Europe. Has everything. Great city, lots to do, gorgeous guys, lots of gay venues and a Sitges, a "gay" beach a short (and cheap) train ride away. Madrid has an even bigger gay club scene but is a different city than Barcelona.
Sydney, Australia is pretty gay friendly as well with lots of clubs and bars. Lots to do as well. Although summer in the US is winter in Sydney.
Those are the top "gay" cities in Europe & the world that I know of that will allow you to go to a variety of places, clubs, bars, saunas, gyms--and still see great sites.