I do not usually gush about entire countries.
I do not work for the Slovenian office of tourism.
2. Lakes: Lake Bled is the more touristy body of water because of its picturesque, church-topped island and a castle that overlooks the lake from a rocky cliff. I caught myself staring at the castle and saying "Awesome" enough times to sound like an authentically dumb Californian to any passerby. Nearby Lake Bohinj is also a natural wonder, with majestic mountains surrounding the western part of the lake. I'm sure there are other lakes in Slovenia, but I didn't see them. It's OK though. I was more than satisfied with these two.
3. Hikes: We hiked as far as we could up Vintgar Gorge which is only 4km from Lake Bled. The hiking path lines a spectacular emerald green river. It was such a wonderful place that I actually felt guilty when I had to pee off the side of the wooden walking path. (Nobody was around) We went on another great hike up to Savica Waterfall near Lake Bohinj. Though the snow pack was so high it was impossible to get close to the falls, it was well worth the icy, 30 minute hike up to the look-out-point.
4. Castles: They're built on top of hills, dramatic rocky ledges, into the sides of mountains (Predjama Castle), and you can see them from the side of the freeway while driving by. Where I'm from, there are no castles, so this common Slovenian sight was quite a novelty to me. What can I say? Castles. They look very cool.
5. Caves: We drove to Postojna Cave at 5pm and couldn't get in because it closed to the public at 4. I'm always late-- story of my life. So I'll have to save this cave and Krizna cave-- and the Venetian town of Piran on the coast-- for the next time I'm driving through this little country. With so much natural beauty, I feel like I need to go back and spend at least a week to explore and appreciate it.