About five kilometers to east of the city of Bishapur, and beyond the reliefs in the Tang-e Chowgan gorge, there's a wide valley between two lines of rocks, some 450-500 meters high. In the northern mountains is, at a height of about 400 meters, the Mundan Cave, which is also known as the Cave of Shapur.
The entrance of the cave is about twenty meters wide and five meters high, but inside, it is much larger and reaches a height of twelve meter. It is hard to discern from the valley, but this picture may be useful. The cave contains a monumental colossus of the Sasanian king Shapur I (241-272), and there is also a well. It has been assumed that the cave was meant as tomb of the king, but this is by no means certain.
Like the representations of the king on the reliefs in the valley (e.g., relief II), the king is shown with long hair, a crown, and all his weapons. When the Arabs conquered Iran in the seventh century, the statue was pulled down and its legs were destroyed. The statue was reerected in the 1930s by Reza Shah.
The best way to go to the cave is to hire a guide at the entrance of the excavation of Bishapur City, and/or ask for a driver from the village in the valley. (Announce your visit well in advance.) You will need at least two hours to drive to the village, climb the mountain, return, and drive back to the entrance of the excavation. The climb is not easy; make sure that you have good shoes.