It’s a great idea to take a daytrip from Trebinje to Kupari if you want to see something unique and enjoy a little beach time as well. Only 5 kilometers from Dubrovnik, Kupari was a former military resort for the Yugoslavian military. Though the beach is still beautiful, the former hotels lay in ruins. If you’re interested in abandoned buildings, you’ll have a fantastic time exploring this area.
Unfortunately, there’s no bus going to Kupari. The easiest way is by taxi, which is about 40 EUR round-trip, depending on wait time. You could also try hitch-hiking, as it’s a mere 25 kilometers from Trebinje.