Plitvice Lakes National Park

Plitvice Lakes is one of the best national parks I've been to anywhere, a chain of terraced turquoise lakes and waterfalls linked by wooden boardwalks. It's inland, off the train network and not near any big city, so you get there by car or bus. The bus is easy enough, and you can buy a ticket at any major bus station, but timetables and seat availability are hard to pin down online. The Balkans don't run on tidy published schedules, so build in some flexibility.

Go at opening. Plitvice is on the same must-see list as the pyramids, and by mid-morning the boardwalks back up like an amusement park queue. One thing to know before you commit: the entrance sits at the top of a valley, and you walk down into it, around the lakes, and back up. It's a lot of stairs and boardwalk, so it's not the right day out if walking and climbing are going to be a problem.