Spent a lovely day on Lokrum after catching the taxi boat from the main port in Dubrovnik which goes very half hour or so in high season. Tickets were 50 kuna for a return trip and entry to the island.
Spent a good few hours exploring the island, climbing the steep hill to the ruins of the fort and exploring the monastery and botanical gardens. The gardens are well worth a look-some amazing plants and cacti there. The island is also home to wild peacocks, which are so used to humans they allow you to get really close to them. We spent the afternoon lazing on the rocks by the sea, cooling off by jumping into the sea every now and again. The waves can be pretty big but there are ladders drilled into the rocks to help you get in and out. There a several cafe bars which also serve food, we brought a little picnic so we didn't try the food but the beer is good and cold!
Would highly recommend for a day trip or even an afternoon as it's very easy and quick to get to.