Slovenia is small enough to cross in a few hours and varied enough that the drive is worth it: Ljubljana in the middle, Lake Bled and the Julian Alps to the northwest, karst caves inland and a short Adriatic coastline near Piran. Most of it can be seen from one base.
The guides here cover Ljubljana and Slovenia overall. Summer opens the alpine routes and fills Bled; spring and autumn are quieter and better for the caves and the capital. Ljubljana's center is pedestrianised and compact, which makes it an easy first stop. Slovenia requires a vignette for motorway driving, bought in advance rather than at toll booths — a common oversight for visitors arriving by car.