One of the most important early archaeological remains in Patna, the Agam Kuan (well) is located close to the Gulzarbagh railway station. The name means unfathomable well and it is widely believed to be associated with Mauryan emperor Ashoka. It is said that the Agam Kuan was part of king Ashoka's hell chambers and used for purposes of torture. Apparently, fire used to emanate from the well and offenders were thrown into this fiery well. A legend says that it is the site where emperor Ashoka killed his 99 brothers by throwing them into the well. His aim was to be the master of the throne of the Mauryan empire.

Another myth says that the bottom of the well is connected to River Ganges. A saint once found a heavy log inside the well which had been lost in the sea earlier and so it was inferred that that the well is connected to the netherworld or patala (hell). There are eight arched windows that offer a peek at the deep waters. Apparently, during emperor Akbar's rule, a roofed structure was built around the well. There are several other fascinating tales related to this well. The Jain monk, Sudarshana, was thrown into the Agam Kuan by king Chand, but legend has it that he floated to the surface, seated on a lotus. The depth was believed to be 105 ft, but during a cleaning project in the 1990s, it was found to be 65 ft. It is said that this well never dries up and the water level fluctuates between 1 and 5 feet.

Devotees throw flowers and coins into this well as it is considered auspicious. In olden times, it is said that gold and silver coins were thrown into the Agam Kuan by Mughal officials.