The Narin Qal'eh or Narin Castle or Narenj Qaleh is a mud-brick fort or castle in the town of Nain, Iran. Structures like these constituted the government stronghold in some of the older (pre-Islamic) towns of central Iran. Some of these castles incorporate mud bricks of the Medes period and of the Achaemenid and Sassanid dynasties
The ruins of the structure stands 40 meters (130 ft) high from its base. Although built some 2000 years ago, it contains what seems to be a type of plumbing system made out of mortar ("sārooj") built into its massive walls. It is also peculiarly similar in design to Ali Qapu palace of Isfahan; it has a terrace high on top of the structure whose circulation is provided by two helical stair wells (whose walls have caved in, making it inaccessible). The structure also has a large underground chamber (filled now by rubble), possibly a prison. Four towers surround the entire compound, and a large gate furnishes access to a large courtyard. The structure seems to have been the victim of numerous earthquakes throughout the ages.