Sinaia is a town and a mountain resort in Prahova County, Romania. It is situated in the historical region of Muntenia. The town was named aft…Sinaia is a town and a mountain resort in Prahova County, Romania. It is situated in the historical region of Muntenia. The town was named after the Sinaia Monastery of 1695, around which it was built. The monastery, in turn, is named after the Biblical Mount Sinai. King Carol I of Romania also built his summer residence, Peleș Castle, in Sinaia in the late nineteenth century.