Croatia?! It's so beautiful. Dubrovnik and the surrounding islands are gorgeous and there's plenty of walking/cycling routes, watersports etc, as well as relaxing beaches! Not sure how wild the nightlife is, but I'm sure if you researched it you'd be able to find somewhere!!!
Also, Greece might be a good idea? Maybe some island-hopping to make sure you get the most of the history, relaxation, activities and nightlife! It's supposedly quite cheap at the minute too?
Hope you find somewhere lovely!! xxx