The Visitor Center in Thissio is located on the Hill of the Nymphs and it is housed in the Sina building (photo on the right). The construction of the building commenced in 1842 after the generous donation of George Sinas, a businessman and ambassador of Greece in Vienna, and led to the establishment of the Observatory of Athens. The building itself was designed by the Danish architect Theophil Hansen. The site is situated across from the Parthenon and just to the north of the hill of Pnyx, where Meton built his heliotrope in the 5th century BC to perform the first astronomical observations of the classical Greek period.

The goal of the Center is twofold: to inform the general public on a wide number of Astronomy related topics and at the same time to present the nearly two century long history of Greek Astronomy and NOA, a history which has been shaped by the major transitional periods in the evolution of the modern Greek state.