Sifi-Nor

Sifi-Nor (Zean: Sandspires) are partial ruins of an ancient city, half-submerged in the south of the Great Eastern Desert. They derive their name from eight towers rising from below the sands.
The Sandspires were found in 50AU by a Nata-Kea expedition into the desert, hoping to find a sefia source alternative to the laborous mining. In 50 AU, the settlement of Safi-Tor was established as a bridgehead base of operations, distant only a day of journey from the lost city.
Sifi-Nor's remnants are dispersed over approximately five square kilometers, assuming there are no short buildings underground filling the distance between visible parts of the city. Most of the Sifi-Nor is being regularly covered by Erjat-Reh lichen, though the colonies are culled whenever possible by Nata-Kea expeditions. The most distinct landmarks are eight spires, forming a curved line through the middle of the area. They seem to be buried several stories deep, yet they would tower over any other known monuments and palaces. The spires are all angled exactly the same way, supporting the theory that they are a part of a bigger structure. On one side of the tower line, several smaller stone outcrops stick out of the sand. On the other, only two were found so far, including the Empty House. 
The Empty House is an oddity among the strangeness that is Sifi-Nor. It is a mostly intact house, which was pushed by the sand currents to the surface of the desert. Several exploration efforts were needed to remove all sand and debris from the house, an effort partially countered by the desert's currents. After removal, only naked walls were left, with no artifacts recovered. The walls themselves, similarily to all the other stone material on the Sandspires, were infused with sefia through an unknown process and retained an incredible degree of integrity. Any attempts to remove stones from the discovery site other than for experimentation at Safi-Tor settlement are prohibited.
The Empty House is the only building that allowed the explorers entrance so far. Attempts to puncture one of the tower walls, allowed after long deliberations, were ultimately unsuccessful even when sefia-infused tools were used, which indicates that a method similar to the one encountered in the Sky Tower was employed. Nata-Kea attempted to excavate one of the towers, but no point of entry was located after three floors were unearthed, and the desert was undoing the efforts at a speed that did not allow for further work. It was postulated that it is actively trying to bury the city back, but no non-superstitious evidence for the claim was found.