Slovenia is, arguably, the cutest of the formerly Communist countries, and Ljubljana is a great little city full of charm. It's pretty easy to have a good time here. It's full of galleries and museums and young artists. The Ljubljanica river flows through the center of town, past Baroque buildings and under the ramparts of the ancient castle on the hill.
The website of the Ljubljana Tourist Board is a good first stop. The city is definitely courting tourism, with an emphasis on cultural travel.