Hisarya is a small spa town north of Plovdiv, at the foot of the Sredna Gora range. Its mineral springs would be enough to make it a Bulgarian health resort, but the reason travelers should care is that the springs sit inside one of the country's most complete Roman urban landscapes.
The ancient town, probably Diocletianopolis, was fortified in the fourth century after earlier destruction. Much of the wall circuit still stands, with towers, gates, baths, a Roman tomb, and park paths running through the old enclosure. The Southern Gate, nicknamed the Camels, is the obvious symbol, but the pleasure of Hisarya is walking the whole area slowly and letting ruins, fountains, and spa-town life overlap.
This is not a loud destination. People come to drink the water, sit in parks, and take treatments. That calm is part of the appeal. Hisarya works well as a day trip from Plovdiv, but it is better with a night if you want the Roman walls after the tour buses and day bathers have gone.