The longest water cave which can be passed through by boat is located 75 km to the north west of Hamedan in the Zagros-mountains and coordinates E48,18.064 , N35,18.303 , h 2100 m.
Alisadr is a limy and acidic cave. Geologists believe this is one of the most wonderful and longest water caves which is formed in the Jurassic period (Second geometrical era 190-136 million years ago). The cave is humid inside, and absolutely silent, its islands and beautiful views can be visited by boat and cavers. The temperature inside the cave is about 16 and the water is always 12 centigrade degree. It is measured from half a meter to 14 meters deep. Water hardness is high, limy and not drinkable. Alisadr is an alive cave and there is no poisonous gas in it and because of the air circulation you will not feel suffocated. There are not any living creatures because of no sunlight.
About 11.3 km of this cave has already been discovered and about 3.2 km can be visited by the tourists which is the longest cave in the world to pass through by boat. Cave has two entrances from North and West. Various colorful stalagmites on the ceiling of this cave is the special feature of it.
You can visit Alisadr cave in all seasons in which the temperature does not change. But it is advised not to go on holidays as it is too crowded. You can also visit other attractions of Hamedan on your trip to this area.