Due to Dubrovnik's location right on the thin southern tip of Croatia, it is relatively easy to pop over the border further south into Montengro. (In fact, many of those who are holidaying in one of the Montenegrin coastal towns find it easier to fly into Dubrovnik.)
Likewise, the border with Bosnia & Hercegovina is also relatively close to Dubrovnik, and there are a number of towns there that are well worth a visit.
Montenegro
Just over the border into Montenegro are a number of coastal towns - and you may like to see what other Adriatic seaside towns are like! Amongst those that are relatively easily reachable are Herceg Novi, Budva and Kotor. The majority of these towns don't really have many beaches to speak of, so if that's the kind of thing you're after it's probably better to plan an different daytrip!
Remember, as you're going into a different country, to double-check if you require a visa for Montenegro at the Montenegro Ministry of Foreign Affairs website.
Kotor Kotor is probably the most worthwhile Montenegrin town to make a day trip from Dubrovnik to, as it's a wonderfully preserved costal town with numerous sights. The bus journey to Kotor takes 1 hour 50 minutes, and it's possible to take a trip here and back in one day. Kotor bus company Autoboka have a bus that departs Dubrovnik at 10.30am, and the latest return bus departs Kotor at 5pm.
Isango also offer an organised tour to the Bay of Kotor, which includes a full days exploration of the area and the chance to indulge in some swimming on this part of the Adriatic. The tour, including transfer time, lasts 12 hours.
Kotor is set on the beautiful Bay of Kotor (along which a number of towns are situated - you could equally stop off at any of them!) and is a UNESCO World Heritage site. Amongst the sights to see are the well-preserved Old Town and its city walls (along which you can walk) and the Cathedral of Saint Tripun (built in 1166).
Herceg Novi
The bus journey to Herceg Novi only takes just over 1 and a half hours, and Herceg Novi is the first larger town you come to after you cross the border into Montenegro. There's an daily early bus at 9.30am (see Dubrovnik Bus Station website.) and another at 10.30am, whilst the last bus back to Dubrovnik leaves Herceg Novi at 3.30pm.
There's plenty of sightseeing opportunities in Herceg Novi, including several fortresses (such as Forte Mare), churches (St Michael Archangel Church and St Jerome Church, both in the Old Town), monasteries and galleries.
Budva
Budva is further south along the coastline, and although it only takes approximately 2 and a half hours (there's a daily bus departing Dubrovnik at 10.30am), there's no late afternoon return options that make this destination viable for a daytrip.
If you do fancy visiting and staying a night (or more), you'll be rewarded with sights including Budva's Old Town, with its city walls and churches. Budva is more famous, however, for its sandy beaches in the city and around it. It is this that makes the place a popular tourist destination - the most popular in Montenegro, in fact. This also means that the city has a bustling nightlife scene.
Bosnia If you are planning on making a trip to Mostar (or elsewhere in Bosnia) please double-check that you don't need an additional visa for this country. You can do so on the Bosnian Ministry of Foreign Affairs website.
Mostar
Mostar is a bit of a journey from Dubrovnik but well worth a visit if you don't mind the extended travel time. There are a few daily buses to Mostar; the 8am bus will get you in early enough (about 11.45am) to allow for about half a day's exploring, as there's buses back at just after 5pm. (And a later, overnight, bus at 1.50am if you want to stay until the early hours!) Bus routes run by Autotrans and Bosnian company Globtour.
Organised tours are available, such as the one from Isango; their Road to Mostar (11.5 hours) tour includes stops at Neum, Metkovic and Pocitelj as well as a full tour of this wonderful Bosnian town.
Mostar is a wonderful town, made most famous by its Old Bridge (Stari Most) over the River Neretva, which was the first single span stone bridge ever built, in 1566. The bridge is how the town got its name, of course - "most" meaning "bridge" in Bosnian, and those that guarded the bridge were called "Mostari" which eventually evolved into the Mostar for the area.
Aside from the Old Bridge, the town has numerous other sights and places to visit including the Old Town, and various mosques and chuches. If you are there during July, the famous Mostar bridge diving competition takes place. Check locally for the exact date of the competition.
Medjugorge
Medjugorje isn't an ideal place to visit using public transport, as the daily bus only departs Dubrovnik after 5pm. (The journey takes about 3 hours.)
If you do want to make a daytrip to Medjugorje from Dubrovnik, it is advisable that you book an organised excursion through a local travel agency. You can also pre-book a tour online; Isango have an 8-hour Medjugorje Holy Tour that includes transfers to and from Dubrovnik, the opportunity to attend mass at the church in Medjugorje, and the chance to explore the town yourself.
Medjugorje is most famous for apparent visions of the Virgin Mary, which have appeared to several people over the years. It is now a popular place for pilgrims to visit as a shrine.
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