Mljet National Park

Listen first. Beneath the pines there is a dry, steady crackle. Needles shift underfoot, and cicadas fill the warm air. The smell is resin and salt together, sharp and green. Through the trunks you can see water so still it looks like glass. It is not a river, and it is not quite the open sea. Welcome to Mljet National Park, on the western end of one of the greenest islands on the Croatian Adriatic coast.

Mljet is a long, narrow island. It stretches across the sea south of the Pelješac peninsula, in Dubrovnik-Neretva County. Dense forest covers much of it, mostly Aleppo pine and holm oak, a dark evergreen oak of the Mediterranean. That forest is one reason the park exists. In 1960 this corner of the island became a national park. It is one of the oldest protected areas along the Adriatic that include both land and sea.

The heart of the park is the water in front of you. There are two lakes here, and both of them are salt water. Locals call them Veliko jezero, the Great Lake, and Malo jezero, the Small Lake. They are flooded karst valleys. Karst is limestone country, where rain and time dissolve the rock into hollows and caves. At the end of the last ice age, the sea level rose and filled these hollows with seawater.

Here is the first surprise. The lakes are not sealed off from the sea. A narrow, shallow channel links the Great Lake to the open Adriatic. Another short channel links the two lakes to each other. Twice a day the tide pushes water in, and then pulls it out again. If you stand on the small bridge between the lakes, you can often see the current running. Sometimes it flows one way, and later in the day it reverses.

Because the lakes are sheltered and shallow, they behave differently from the sea outside. In summer the water often warms faster than the open Adriatic. Many visitors swim here for exactly that reason. In the deeper parts, the water still holds a cool layer below the warm surface. Divers and biologists have long studied these layers. The lakes also shelter sea creatures that prefer calm water, away from waves and boat traffic.

Now look out across the Great Lake. In the middle sits a small, wooded island with pale stone buildings and a bell tower. This is the island of Saint Mary. In the twelfth century, Benedictine monks came here from the Italian coast, from a monastery in the region of Apulia. They built a monastery and a church on this tiny island. For centuries, monks lived and prayed here, surrounded by water on all sides.

Think about that choice for a moment. An island, on a lake, on an island. It was a place of deep quiet, but it was also a place of power. The Benedictine community held land on Mljet and played a part in local life for generations. Over the centuries the buildings changed with new owners and new uses. Later periods added walls, rooms and repairs. Today the church and monastery sit restored on the little island, and a short boat ride carries visitors across.

The monks were not the first people to value this coast. A short distance away, in the village of Polače, stand the ruins of a large late Roman building. Its thick stone walls still rise above the waterfront houses. Historians link this period to the time when Roman power reached across the whole Adriatic. Polače's deep, protected bay made it a natural harbour, and that is still how the village lives today, with boats tied up beside ancient stone.

Mljet also carries legends, and they are best heard as legends. According to one popular tale, this is Ogygia, the island where the nymph Calypso kept Odysseus for seven years in Homer's Odyssey. Locals point to a sea cave on the island's southern coast as Calypso's cave. Another local tradition says Saint Paul was shipwrecked here, not on Malta. Scholars debate both stories. But on a quiet evening by these lakes, it is easy to understand why people wanted to tell them.

Here is the second surprise, and it involves an animal. In the early twentieth century, people brought the small Indian mongoose to Mljet. The aim was to control the venomous snakes on the island. The mongoose stayed, and it spread. Today you may see one cross a path in a quick brown flash. The story shows how a single human decision can change an island ecosystem for more than a century.

The best way to know the park is slowly. A path runs around much of the Great Lake, flat and shaded for long stretches. You can walk it, or rent a bicycle in the villages of Pomena or Polače. Kayaks let you glide close to the reeds and the rocky edges. Small villages such as Govedari sit up in the hills, among vineyards, olive trees and dry stone walls built by hand over generations.

As you move around, notice the edges of the water. Where the lake meets the rock, the limestone often shows a worn, grey band. That band marks the range of the tide and the work of salt water over thousands of years. Notice too how colour changes with depth. Near the shore the water is pale and clear. Farther out it turns to deep green, then to dark blue where the lake floor falls away.

The light here changes the whole place through the day. In the morning, the lakes are often flat as a mirror, and the pines stand doubled in the water. By midday, the sun is hard and white, and the shade under the trees becomes precious. In the late afternoon, the light turns gold on the monastery walls. A breeze may roughen the surface, and the reflections break into small moving pieces.

Before you leave, stop for a moment by the water. Listen to the cicadas again, and to the soft knock of a boat against a jetty. Look at the island of Saint Mary, small and patient in the middle of the lake. Monks, sailors, fishermen and storytellers have all stood on these shores. Now it is your turn. As you walk back under the pines, notice the resin smell in the warm air, and the glint of salt water between the trees.