In the vicinity of Gamzigrad lie the ruins of a huge Roman complex called Felix Romuliana, one of the most important late Roman sites in Europe. Early explorers believed the ancient ruins to have been a Roman military camp, because of their size and numerous towers. Systematic archaeological excavations conducted since 1953 revealed that the site was, in fact, an Imperial palace. The name Felix Romuliana was given in memory of his mother Romula, who was also a priestess of a pagan cult. The complex of temples and palaces served three main purposes - a place of worship of his mother’s divine personality, a monument to his deeds as emperor, and a luxurious villa for Galerius.
source: https://en.wikipedia.org/wiki/Gamzigrad
If you ever travel to this part of Serbia, this place is definitely worth seeing!
And you can log a geocache as well! It is a small plastic photo film canister with a logbook - bring a pen! The box is hidden in the hole of a tree on the left side of the road - marked with trekking mark (see photo hint).
Happy geocaching!
NOTE: the owner can re-visit the location only 2 times a year.