Dar Al-Hajar; The Rock Palace; stands atop a protruding rock formation in Wadi Dhahr, a fertile and pleasant valley of small villages and clay-walled orchards. Pictured in many books about Yemen, it has become a symbol of the country itself.
Dar Al-Hajar is located at the western suburbs of Sana'a in the famous Dhahr valley, and is truly a Yemeni architectural wonder. The palace represents architectural excellence and shows how people cope with nature and turn its complications into man-made monuments. All this unfolds to whoever visits Wadi Dhahr; on an overlooking mountain peak, one can see a huge palace built on top of a rock in the heart of the valley which is surrounded by fruit trees.
Although built as a palace and not as a primarily military structure, the vertical sides of the rock on which it sits mean that any asssault on the dar al-hajar would have been far from easy. The palace also has its own water supply from deep below the rock and could therefore have easily withstood a siege.
You can see a photo of the palace in the comment below...