The citation for the asteroid reads:
(90718) Castel Gandolfo = 1991 RW3
Discovery: 1991-09-12 / F. Börngen, L. D. Schmadel / Tautenburg / 033
Castel Gandolfo is a small Italian town and the summer residence of the popes. The headquarters of the Vatican Observatory are located in the town.
The discovers of this asteroid make for an interesting story themselves:
Freimut Börngen (17 October 1930 – 19 June 2021) was a German astronomer and a prolific discoverer of minor planets. He is credited by the Minor Planet Center with the discovery of 538 numbered minor planets made between 1961 and 1995. – Wikipedia
Lutz Dieter Schmadel (2 July 1942 – 21 October 2016) was a German astronomer and a prolific discoverer of asteroids, who worked at the Astronomisches Rechen-Institut (ARI) of the University of Heidelberg. He is credited by the Minor Planet Center with the discovery of 245 minor planets made between 1960 and 1993. – Wikipedia
Lutz Schmadel was the author of the Dictionary of Minor Planet Names – a reference book containing information about the discovery and naming of many thousands of asteroids.
I did some inquiry and found that the proposal for the name for asteroid Castel Gandolfo came from Freimut Börngen, who unfortunately died in June of 2021, before I was able to contact him about this asteroid. If anyone has any information on these two astronomers, and any involvement they had with the Vatican Observatory, please contact me!