Technically easy and super beautiful, starting from and ending at the Gorna Banya subway station. It passes through forests, open fields ("Bonsovi polyani"), Gorna Banya monastery, and the Dupevitsa peak (the highest in the Lyulin mountain). It's amazing in autumn! It's a bit long, but the loop could be shortened, e.g. by just going to the monastery only.
Done on 2021-10-29. Actual route, done as a trail run: https://www.strava.com/activities/6183083504 (There is good forest path that avoids some walking through the town and you might want to use it.)