From the Sultan Sanjar Mausoleum, drive due west, leaving Sultan Kala through the western Firuz Gate. South of the road, the small reconstructed square mausoleum, open on all sides, is known as Kyz Bibi. Some scholars have suggested that this may be the burial place of Sultan Sanjar's wife, Turkan-khatun. Who was not a fairy bird, then.
The next turning to the south takes you to two fascinating monuments. The Greater and Lesser Kyz Kalas are two isolated buildings known as koshks, which have distinctive corrugated exterior walls. The Greater Kyz Kala is rectangular in plan, with a length of 45m and width of 38m. Its corrugations are well preserved on the eastern and southern sides of the building, protected against the prevailing wind. The interior of the building preserves squinches and traces of different kinds of vaulting. The Lesser Kyz Kala stands a couple of hundred metres due south: it is roughly square in plan, with sides 20m long, and is more poorly preserved than its neighbour, though does retain the remnants of a stairway in its southeast corner.
'Kyz Kala' means 'Girls' Castle': one story runs that forty girls hid in the Greater Kyz Kala at the time of the Mongol invasion. When they saw what the Mongols had done to the inhabitants of the city of Merv they committed suicide by jumping from the roof. Another local tale identifies the Greater Kyz Kala as the castle for the girls; its smaller neighbour as the boys' castle. It is said that young men wishing to marry the girl of their dreams should fire a projectile from the southern castle, to land in the northern one. Given the distance between the two, there are presumably many local bachelors.
The buildings were elite rural residences, and probably date from the 8th or 9th centuries. There remains much debate about the purpose of their distinctive corrugations: theories include helping to keep the interiors cool, ensuring the rapid run-off of potentially destructive rainwater, and simple decoration.