Tharmida

The Tharmida oasis fort (also spelt Tharmada'a or قصر العناقر الأثري in Arabic on Google Maps) is a fort in a small city in the Arabian desert 160km northwest of Riyadh, 30km southeast of Shaqra. The fort measures about 30m x 40m and is in a good shape. The outer walls are clean and without cracks, which means that the fort has been restored recently. It's unclear what the opening hours are - at the time of visiting the fort was closed and other travellers have reported also finding the fort closed.
The fort is also known as the Al-Anaqer palace. It was built by Prince Ibrahim bin Suleiman Al-Anqari in the year 1723. The palace is surrounded by a deep trench on three sides: the northern side, the eastern side, and the southern side.
How to get to the Tharmida fort
The Tharmida oasis fort can be easily reached by car (two hours from Riyadh, 25 minutes from Shaqra).
Accommodation
The closest hotels probably are those in Shaqra, some of which are bookable with the international hotel booking portals.