The town of Škofja Loka is on the way from Ljubljana to Bled if you take the "scenic" route and not the fast highway. The drive from Ljubljana to Škofja Loka is nothing special, but from Škofja Loka to Bled through the hills and little towns offers breathtaking scenery. Škofja Loka itself is a delightful little town, well worth a stop as well.
I enjoyed the Julian Alps loop drive (I did it myself) - pretty much followed Rick's suggestion (counter-clockwise direction, from Bled).
Piran is a beautiful coastal town - probably crowded in June but sparkling at dusk and at night.
I visited the Škocjan Caves (the harder one to visit by public transportation) and I was slightly underwhelmed - not that the caves themselves and the crystals etc. aren't amazing, but it is a lot of time and effort to get there. I enjoyed my above-ground experiences in Slovenia much more. If you have a fascination with caves these would be worth a visit for sure, though.