On the top of Mountain Oche and in other places of southern Euboea, 23 megalithic buildings are preserved in relatively good condition. They are known as “Drakospita” (= Dragon houses); their builders and purpose are unknown. We postulate that they, and especially the best-preserved one (that of Oche), were buildings dedicated to the worship of Teleia Hera (the “Perfect Hera”), the protector of marriage. According to the local tradition, these structures were built by dragons and here resided the king of the Cyclops. We believe that the true constructors were the Dryopes, an ancient prehellenic tribe worshipping Hera, a goddess associated in a certain mythological tradition with the celestial phenomena. In March 2002 and July 2004 we visited the Drakospito of Oche, measured its dimensions and calculated its orientation based directly on the Sun’s azimuth at sunset. A Sirius-rise orientation corresponding to circa 1100 B.C., not at odds with a previous archaeological dating based on artefacts found inside the structure, indicates a religious / celestial purpose for the building, in contrast with previous theories that it was merely a lodging built for shepherds, quarry workers or stone-cutters. In fact, it could be argued that at least the Drakospito of Oche was not mainly a place of Hera’s worship, but also an ancient megalithic prehellenic observatory of the celestial phenomena.