Mljet was originally one of the Roman possessions (indeed, Polače means "palace" and holds some Roman Ruins). Over the course of history, traded hands with the rest of the Balkans (to the Ottomans, the Austro-Hungarians, etc.) It was even promised to Italy at one point in the early 20th century. Once the Kingdom of the Serbs, Croats, and Slovenes was declared, the Island became part of that group.
Over 72% of the island of 388 square miles is forest. The island's geological structure consists of limestone and dolomite forming ridges, crests and slopes. A few depressions on the island of Mljet are below sea level and are known as blatine ("mud-lakes") or slatine ("salt-lakes"). During the rain seasons all blatine are filled with water and turn to brackish during dry seasons. The island is really hilly - if you plan to spend some time there strongly consider renting a car or a scooter.
The climate is Mediterranean; an average air temperature in January is 48°F (9°C) and in July about 75°F (24°C).
National Park entrance fee
There is an entrance fee of 125kn per person (40kn for students with id-card) to enter the Mljet National Park. If you are joining an excursion organised by a travel agency to Mljet, it may not include this entrance fee, so make sure you check before booking.
The Nona Ana catamaran  operates twice daily from Dubrovnik to Sobra and Polače on Mljet island. Tickets are 54kn one way per person. Polače is nearer the National Park than Sobra.
There is car ferry operating five times a day between Prapratno on the Pelješac peninsula and the port of Sobra on Mljet island.
There is car ferry from Split on Saturday and speed boat from Lastovo on Tuesday and Thursday.
From Korčula you can get to Sobra on Mljet island by car ferry operated by Jadrolinija  on Tuedays and Saturdays. The ferry leaves Korčula Town at 2pm and arrives at Sobra at 4:15pm. Note that Sobra is some distance from the National Park, which is located on the western side of Mljet island. Alternatively, join a day trip excursion from Korčula organised by a travel agency:
With all tours make sure you ask if they have numbers to run the transfer/tour. They often cancel without notice.
It is hard to move around Mljet without a car or a scooter because of the island's hilly terrain. There is only one major road on Mljet which runs through or near most towns. The road is paved but only suitable for faster driving in only a very few places. The speed limit is often 40 kph. For most of its length, the road has long uphill or downhill parts. If you come without a car, you can rent one at several local agencies. Expect older used cars. The only petrol station is at the Sobra ferry terminal.
Swim around, snorkel and try to find the large mussels (about 2 feet long) in the smaller lake (Malo jezero). Look but don't touch - they are protected! Rent a canoe at the bridge at the smaller lake and paddle to Soline. You can even stop at the island and visit the monastery. The whole trip takes about three hours.
There are several places to eat out in Pomena, around the harbour. Most appear to cater to the yachting fraternity and specialise in very fresh fish; live seafood are kept in tanks next to each restaurant. There's also a great restaurant between the harbour and the hotel. It looks like it's a private house but with a large barbecue area built on, and it does excellent barbecued fish. Besides that, there are restaurants in most of the villages: Polače, Soline, Babino polje, Prožurska luka, Okuklje, Saplunara. There is also a restaurant on the island of St. Mary.
There's not a lot of nightlife in Pomena; the hotel has an inside bar with a cheesy band, and an outside shack that sells drink. It's best for a quiet getaway rather than a party!
There used to be poisonous snakes on Mljet once but in last half of 20th century, Indian Munogs animals were introduced and poisonous snakes are not to be found on Mljet nowdaays. If you plan a hike, make sure to bring a solid pair of sneakers or shoes and as always, plenty of water. There is good cell phone coverage. Keep in mind that Mljet is sparsely populated.
In summer days speed boat goes from the port of Sobra to Dubrovnik every day at 6:15 a.m. (Tuesday and Thursday at 6:00) and at 17:35. From port of Polače speed boat goes every day at 4:55 p.m. From Sobra car ferry goes every day to Prapratno (peninsula Pelješac) at 6:00, 9:00 a.m. and at 12:00, 16:00, 19:00 p.m. (on Sunday and holiday goes at 10:00 a.m. not at 9:00). With speed boat you can also go to island Korčula from Polače and Sobra on Monday, Tuesday, Thursday and Saturday, and with car ferry from Sobra on Monday, Wednesday and Saturday. There is speed boat from Sobra and Polače to island Lastovo on Tuesday and Thursday. To Split you can go from Sobra with car ferry on Saturday.