Just before the town of Petrich, rise the rugged slopes of one of Bulgaria's most interesting geological formations. The Kozhuh Planina is too low to class as a mountain but is the most spectacular remains of the crater of a volcano whose last eruption was a million years ago. Mineral springs abound here, too, filling the air with steam and the smell of sulphur.
In the past two decades the Kozhuh Planina has been the witness of the increasingly popular cult of a local blind clairvoyant, Vanga, who spent her last years in the nearby Rupite area.
But here is also something for the archaeology buff. Between the 4th Century BC and the 4th Century AD, on the southern slope of the Kozhuh Planina Heraclea Sintica lived and prospered. Its name is preserved in ancient historical accounts, but until recently historians were at a loss as to its actual location. In 2002 a stone inscription mentioning the name of Heraclea Sintica was discovered at the Kozhuh Planina. The lost town was found.
Excavations of Heraclea Sintica began in 2007, and each year new discoveries are made, including about how the town was abandoned. It probably happened in 388, after a powerful earthquake.