The Apostolic Palace of Castel Gandolfo is located at the borders of Lake Albano which is formed by two small volcanic craters with a max depth of 170m and measures 3,5x2,3km.
Interesting however are the 4 observatories located at Castel Gandolfo. Two of them are part of the Pope's Palace and two are located within Papal Gardens.
According to the information I found the Observatory's Headquarter is still at Castel Gandolfo, however the telescope's from the palace are moved to Arizona. It's not clear for me what's inside the domes in the Papel gardens. Some refering to a 26¨ f/3,7 Schmidt telescoop in one dome and in the other dome the Carte Du Ciel telescope (Astrophotgrafy Aperture 33cm, focal Length 3,43m). The Vatican was part of the Carte Du Ciel Project together with 19 other observatories, including the one in Uccle.
Anyway the location is very beautiful and I clearly understand why this is vacation retrait of the Pope.
See also this website for the http://www.vaticanobservatory.org/
