Mljet is the most southerly and easterly of the larger Adriatic islands of the Dalmatia region of Croatia. Mljet lies south of the Pelješac peninsula, from which it is divided by the Mljet Channel. Its length is 23 miles; its average breadth 2 miles. It is of volcanic origin, with numerous chasms and gorges, of which the longest, the Babino Polje, connects the north and south of the island. Port Polače (It. Palazzo), the principal harbour in the north, is a port of call for tourist ferries. Mljet contains one hotel - The Odisej (from the Greek Odysseus) in the north-west corner of the island.
The northwestern part of the island includes an inland sea as well as a small island within it. It has been a national park since November 12, 1960.