The Niasar Fire Temple (called Chahar Tagh) is a structure with a dome over a rock at the highest point of Niasar village, located 28 kilometers west of Kashan in Isfahan Province. The fire temple can be seen from quite a distance and has remained relatively intact since the time of Sassanid dynasty. It is accessible via a road going towards the stone mine goes past the fire temple. This stretch of road has become rugged and bumpy as a result of the transport of heavy duty mining equipment to the region.

The fire temple is 14 by 14 meter building which contains a chamber with a dome over it. There are no walls on the four sides of the chamber. The fire temple has been made of stones put together with a mortar of plaster. The stones used in the lower part of the building are normal and those used in the arches and in the upper parts are square-shaped, looking like big bricks. The lower parts of the building have been coated with plaster in recent years. All walls surrounding the fire temple are likely to have been decorated with stucco carvings in the past.

The main dome of the fire temple had previously collapsed and it was reconstructed in the Pahlavi era. However, the dome of the temple has been modeled on Islamic era domes while according to the famous French archaeologist Andre Godar, the main dome had been like an egg. There is an interesting point in the structure of the fire temple and that is some of the stones used in the building has an older and different cut than others. This stones had been quarried from a cave down the temple for use in the construction of the fire temple. This reveals the fact that the Niasar cave is older than the fire temple.

Generally there would be a number of other premises around fire temples where Zoroastrian monks gathered together for worship. Although it is not known whether this building was used for this purpose, there are rows of stones laid together near the fire temple which are remnants of a building belonging to the Sassanid era. Since the fire over the Niasar penthouse could be seen from distance, the building might have had a symbolic role.

Magnificent premises used to surround the fire temple of which only some small pieces of stone can now be seen on the ground. A few meter down the fire temple, a spring of cool and clear waters flows through the Talar mosque and goes on to the village. It is surprising that running waters exit beside many other fire temples. Some of them bear signs of worshiping Anahita, the goddess of cultivation and fertility.

In year 2000, Reza Moradi Ghiasabadi, the archaeologist, forwarded a theory about the function of the Niasar Fire Temple, as a calendrical monument that works with sunlight. According to him, in each season the sunrays protrude from different angles and with them one can tell the time of the year.

The Niasar cave is thoroughly man-made (except for one or two natural chambers near the entrance openings). No doubt that the cave had been a Mitra temple. Its first cut possibly dates back to the Parthian era. Most Mitra temples like the Niasar cave have been built in full darkness. This cave has other entrance openings, some of which are located inside a rock which separates the upper parts of Niasar from the lower neighborhoods. These openings which face the north along with the Niasar water fall make a beautiful scene visible from the village.

The sign of water erosion on the rocks bears testimony to the fact that the cave had been a scenic area in the times immemorial. The Niasar water fall is another proof that the cave had been a temple belonging to the followers of Mithraism. Down the water fall, there are two millstones and surprisingly one or two similar millstones can be seen deep inside the cave.

The cave had a big entrance opening which was destroyed in the 1980 earthquake. Parts of the cave were also collapsed onto the gardens located below it in the quake. Most earthenware objects inside the cave date back to the Sassanid era and some belong to the Parthian period. However, some Islamic era pottery works can be seen around the openings of the cave.