The amazing and strange Alisadr Cave, located 75 km from Hamedan, is the longest and biggest water caves in the world. The cave formed at the Jurassic period (about 190-136 million years ago). The cave was originally discovered during the reign of Darius I (521-485 BC) which can be verified by an old inscription at the entrance of the tunnel. This cave attracts millions of visitors each year.
Unlike many other aquatic caves, the body of water in Alisadr is not a flowing river, but rather an extensive, web-like lake. Visiting the cave is done by boat, on the river that flows through it. The cave’s water canals are 11 kilometers long, or at least this is what has been discovered so far. Archaeological studies also revealed ancient artworks and jugs that are 12000 years old. The hunting scenes on the walls, the bows, and arrows found here suggest that the cave was used by the primitive man as a home. The temperature of the cave is always the same 16 is the air and 12 the water.PH is almost neutral and depth of water is measured between 0.5 to 14 meters.
The width of the cave varies between 1.5 and 60 meters. In some sections the caves’ ceiling, more than 15 meters high, is covered with most beautiful cabbage-Iike stalactites hanging downward. Stalagmites soaring toward the roof can be seen in certain parts of the cave invert. There are some dry spots along the network, which are called islands. Fluctuations of water level (50-100 cm) can be seen from the marks left on the surrounding internal rock surface.
Colorful, glittering geological structures cover the tunnel walls above and below the surface of the water, which is clear enough to provide visibility to a depth of five meters. Tight, winding passageways branch off endlessly from one another, or open up into massive rooms like the Wedding Room (also called the 1000 Stalactites Room), the Island (which sits at the center of the complex), and the 600-meter-long Freedom Hall (the largest chamber in the network).
The standard tour takes visitors on a 2100-meter journey through Alisadr Cave, 1470 meters of which is covered by boat—making it one of the longest underground boat trips in the world.