If you are visiting Pirin, I doubt that any of the readers of this blog is interested in the 300 species of mosses and algae from this site.
Instead of just driving around, an alternative is to visit Baikousheva Mura, the oldest or second oldest tree in Bulgaria, dating to over 1300 years old. This also makes it one of the older trees in Europe. It was named after the forest ranger that found it and its a Bosnian pine tree. You can Google to get images of this giant.
To get there, you first get to Banska, a huge ski resort that detracts from this WHS. Then you need a car rental or taxi and head up the road up the mountain. I suspect there is only one road up. The destination is Banderitsa Chalet which is 16km up the mountain and its an apres ski tavern. Banska is at about 900m ASL and Banderitsa is above 1900m ASL. I was there in early May and by 1500m, there was still a lot of snow on the ground. Fortunately, the roads were clear all the way until Banderitsa.
Once you get there, the path to the tree is behind the chalet and its supposed to only be a ten minute hike up the hill. Unfortunately the snow was still deep and we only had street shoes. Having come all this way, we made our way up sometimes knee deep. It took twenty minutes and destroyed our shoes!
Once you come close, there are wooden steps up to the tree so that visitors do not damage the ground and the huge root system. This tree is huge! It has a height of 26m, 7.8m in circumference. Not close to the American Redwoods but big enough for a lot of photo-ops. At this elevation, the mountains were also pretty with snow caps. Great way to tick this site off.