In reply to Dave McKechnie:
Slovenia is great but a beast of a drive, so only worth doing if you visit Austria and maybe Italy. I drove Dovje (northern Slovenia) to Dunkirk yesterday, and it took around 14 hours.
Bear in mind there are a *lot* of roadworks on german autobahns at the moment. They seemed far worse going S than N.
[edit] On activities: The country has good walking, some via ferrata (mostly easy mountain type), hard sport climbing, good kayaking/rafting rivers, amazing lakes, friendly people and good food & wine.
Downsides: Long way, and hard to get good info in english.
Post edited at 18:25