Just back from 2 weeks in Slovenia. The mountains in and around Triglav national park are spectacular, like a condensed Yosemite or Glacier National Park. However, like these parks the riding is limited to primarily fire/dirt/gravel roads. I didn't find too many single track trails and when I did they were pretty rocky and technical. I'm happy to reply to anyone interested in more detail on riding in Slovenia.

I would recommend Luka's Bikes in Maribor for bike rental. Luka set us up with a brand new Scott Genius 960 and a Scott Spark along with a trunk mount bike rack.

Luka's bikes - Trgovina s kolesarsko opremo Maribor