Although not exactly replicating the voyage along the River Styx (the waterway into the Greek underworld), the journey into Golubovitsa Cave is a challenging and similarly aquatic one. Located 3km south of Uhlovitsa Cave, off the road between Smolyan and Mogilitsa, the cave is only accessible by boat, as the first 25m or so is completely underwater. After that, you walk by lantern-light. Special equipment and a guide is essential; ask at Smolyan's tourist office.