The Aladzha Rock Monastery
The Aladzha Rock Monastery is a set of caves hewn into a limestone cliff at the top of the hill in Zlatni Piasatsi's Nature Park, about 3 km west of the resort.
The construct dates back to the era of the Second Bulgarian Empire in the 12th to 14th centuries and would have been inhabited by hermit Orthodox monks.
The word "Aladzha" means "colourful" and the Monastery was so named due to the wall paintings and mosaics which it used to contain. These unfortunately haven't withstood the elements over the centuries but there's a small museum onsite where they have rescued what they could.
The complex is open to visitors from 10 - 5 Tuesday to Sunday during the summer and closed on Sundays in the winter. Standard entrance fee was (Nov 2009) 5 Leva which includes the museum.
On our visit it was a very misty afternoon and so I didn't manage to get a decent overall pic but the website below has a nice little gallery: