The most famous natural phenomena in Zanjan Province is Katale Khor Cave means " mount of Sun"
It's situated at ~120km south of Zanjan city & 410km away from Tehran.
170,000,000 years old in 7 store first 5 stores & 13km of this cave is explored.
They believe this cave join to Ali Sadr cave in Hamedan province.
first 2 km is ready for visitors.& a special way for Rock climbing.