Zmeevi dupki, "the Dragon Holes", is a cave and natural landmark in the Sliven mountain, Eastern Balkan, within the lands of the town of Sliven, at about 350 m, below Karandila.
The protected site covers shallow karst formations about 200 m long. It was declared a natural landmark in 1969 and covers 0.78 ha. The cave is a winter roost for rare bats, above all the lesser horseshoe bat. The Sliven mountain is rich in karst: besides Zmeevi dupki there are the Haydushkata, Mochurite and Orlovi dupki caves.
The cave is closed to visitors to protect the bats. Zmeevi dupki is part of Sinite kamani Nature Park. Up on Karandila, about 2.5 km northeast, is Karandila hut.
Zmeevi dupki is located in Sliven, Bulgaria.
Zmeevi dupki is most easily reached by car. Use the coordinates above to navigate, or open the location in OpenStreetMap or your preferred maps app for turn-by-turn directions. Public transport options vary by region — for remote destinations a rental car gives the most flexibility.
Caves can be visited year-round — the temperature inside stays roughly 10–12°C regardless of season. Spring and autumn are quieter than peak summer. Bring a warm layer and sturdy footwear; some caves close in winter when access roads become impassable.
Access to caves varies. Show caves typically run guided tours during posted opening hours; wild caves require proper equipment and experience. Inside, the temperature stays cool year-round (~10–12°C) — bring a warm layer, sturdy non-slip footwear, and a torch even on guided tours.
