Arecibo Observatory contains the William E. Gordon radio telescope, the largest single-dish radio telescope in the world. The Arecibo Observatory is located about 12 miles south of the city of Arecibo in the north central region of Puerto Rico very close to the Rio Abajo State Forest. The observatory is part of the National Astronomy and Ionosphere Center and operated by SRI International and it accepts and evaluates proposals for its use from the general scientific community.
There is a visitor center, called the Angel Ramos Foundation Visitor Center, that is generally open from 9am to 4pm Wednesday through Sunday. The visitor center is also open on Mondays and Tuesdays during the peak seasons in the summer and around Christmas.
The observatory is built in a limestone sinkhole common in the area called a Karst sinkhole. It was opened in November of 1963 and provides radio astronomy, radar astronomy, and aeronomy capabilities to scientists across the globe.