This is a good few hours drive from Mashhad. But the drive is nice, through the mountains and clouds. The only monument worth seeing is Nadir Shah's treasury. He deposited the loot he had captured from India at this location. The treasure house is built of Maragha marble. The treasury is interesting, but there is no museum or other sight other than the building itself.
The Encyclopedia of Islam, describes this as, 'the most famous fort of Central Asia'. Qilat e Naderi is a high valley, which is a natural fortress with unscalable rock on the north and south. In 1381 Timur launched unsuccessful attacks on Qilat e Naderi.
Nader Shah, is an enigmatic figure in Iranian history. Although he restored national independence and effectively protected Iran's territorial integrity at a dark moment of the country's history, his obsessive suspicions and jealousies plunged Iran into political turmoil, and after his assassination in 1747 the Afshar dynasty he established proved short-lived. A Sunni by upbringing, he was nevertheless a great benefactor of the Shrine of the Imam Reza (a.s.) in Mashhad, which he made his capital. link
Ref: Price, Massoume (2005). Iran's Diverse Peoples: A Reference Sourcebook. [online]. Santa Barbara, CA: ABC-CLIO.
An early 20th century account of a visit to Qilat-i-Naderi
The Mukbarra (Treasury) is an octagonal building with rooms built round a lofty central chamber which rises high above the rest, is surrounded by sandstone columns-not fluted, as some accounts state and was evidently at one time roofed in with a dome. The dome has long since fallen in and the central chamber is open to the sky. The occasional thud of falling masonry detached by the heavy rain that fell during our stay intimated that the process of decay continues rapidly, and made our quartersf eel none too safe. Some of the stone panels of the lower part of the building are decorated with patterns in relief of trees and flowers similar to those seen on the Mogul buildings of Delhi and Agra, but of very inferior workmanship. Below ground-level are the vaults which formerly contained the treasures amassed by Nadir Shah; the entrance, on the east side, was choked with masses of rubble.
J. K. Tod (1923), Kalat-I-Nadiri, The Geographical Journal, Vol. 62, No. 5, pp. 366-370
The Geographical Journal, Vol. 62, No. 5, pp. 366-370