Mljet
The wooded western third of a long Dalmatian island — two tidal saltwater lakes, a Benedictine monastery on an islet inside one of them, and Croatia's first marine protection.
Mljet is the greenest island in the Adriatic — something over seventy per cent forest, mostly Aleppo pine and holm oak — and the national park covers its western third, declared in 1960 as the first protected area in the Croatian Adriatic to take the sea in with the land. Fifty-four square kilometres, about half of it water, on an island long and narrow enough that the park is never more than a few kilometres wide.
Its centrepiece is a pair of lakes that are not really lakes. Veliko and Malo jezero are flooded karst depressions connected to the open sea by a narrow channel at Soline, and through it to each other by an even narrower one — so both are salt, both rise and fall with the Adriatic tide, and a current runs through the bottleneck between them fast enough to swim against. The Romans widened the outer channel; the effect of the connection is a body of warm, sheltered, fully marine water sitting inland among pine forest, which is an odd thing to come upon on foot. In the middle of Veliko jezero is the islet of Sveta Marija, occupied since the twelfth century by a Benedictine monastery, its church Romanesque with later Renaissance work around it, reached by the park boat.
The island collects stories. A cave on the southern coast near Babino Polje has been identified since antiquity as Calypso's, where Odysseus was detained seven years — a claim Mljet shares with several other Mediterranean islands and presses harder than most. Less romantically, the small Indian mongoose was released here in 1910 to deal with the horned viper, in one of the earliest deliberate biological-control introductions in Europe; it dealt with the vipers and then with a good deal of the island's ground-nesting birdlife, and it is still there. The park's forests, meanwhile, are the reason the whole island reads dark green from the sea while its neighbours read grey.
What's worth knowing before you go
Mljet is reached by catamaran from Dubrovnik to Polače or Sobra, or by car ferry from Prapratno on the Pelješac peninsula to Sobra; Polače and Pomena, at the park's edges, are the two places to stay. The island is long, so check which port your boat uses — Sobra is well outside the park and an hour's drive from it. Bicycles are the right way to get around the lakes; the circuit is flat and mostly car-free. May, June and September are best, and the sea in the lakes stays swimmable later into autumn than the open coast because the shallow basins hold their heat.
The connoisseur's hour is early morning on the channel at Mali most, the bridge over the strait between the two lakes, when the tide is running: the water moves through visibly, the pines come right down to it, and the monastery on its islet is still in shadow across the water.