The layout of the Ropotamo Nature Reserve resembles a pirate's treasure map, featuring landmarks like the Lion's Head, Snake Island and Oil Cape as well as a place with the strange name of Beglik Tash.

Ropotamo does have plenty of treasures. But they have nothing to do with pirates and are - literally - priceless. The reserve, spanning 2,500 acres on either side of the eponymous river, which rises in the Strandzha Mountain and flows into the Black Sea north of Primorsko, is home to 257 species of birds. The Red Book of Bulgaria lists 71 of them and The Red Book of the World cites eight. It's also the natural habitat of rare and valuable plants, like the sea wormwood as well as sand and water lilies decorating the area's rocky coves. The area is home to an alluring combination: a Thracian megalithic sanctuary often compared to Stonehenge, the beaches of Arkutino, the thick Strandzha oak forests inland, the exotic liana-covered groves along the river and cacti on Snake Island. It's the kind of place that merits more than one visit.

The Ropotamo's environs resemble a virgin corner of paradise. In the past, however, when the Black Sea's merchant ships passed through the area, they had a much darker glory. Local legends say that it was named Zeytin Burun in Turkish, Elia in Greek and only acquired its present name, which is very similar - Oil Cape - because of the number of ships laden with olive oil that sank near the rocky and inaccessible Maslen Nos.

Not all ships carried olive oil. Some of them were loaded with gold and pirates cheerfully plundered it. A local legend says that they hid their booty on nearby Snake Island - one of the five islands off Bulgaria's Black Sea coast - north of the Oil Cape, in the Bay of Arkutino.

Treasure hunters have dug up every inch of soil covering the small piece of rock looking for the stash of the legendary noble highwayman and pirate Valchan Voyvoda. No one knows what they found. Today, the St Toma Island, as it is also known because it contains the remains of a chapel, is more famous for its cacti. It is the only place in Bulgaria where the exotic plant grows in the wild. They were brought from Bratislava by King Boris III in 1933 and several decades later the Opuncia took over the whole island. Their yellow blooms in spring lend the area an even more picturesque appearance. So why isn't the island called Cacti Island? Instead, it's named after indigenous water snakes feeding off the fish in the sea and in the mouth of the Ropotamo, a mile to the south.

The river, whose name, according to some theories, is a shortened version of the Greek Kalugeropotamos, or the Monk's River, is not among the longest in Bulgaria. It measures only 50 kilometres, or 31 miles, from its source in the Bosna Ridge of the Strandzha to the sea.

Relatively important to the country's economy, it does not flow down breathtaking canyons. However, the Ropotamo is one of the few places in Bulgaria where water lilies grow. And when you sail downstream on the tourist boat (you can take it from the quay by the bridge on the Sozopol-Primorsko road), you will understand why the Ropotamo was declared a protected area as early as 1940. Its shores are covered with oak, ash, elm and alder trees. Wild vines and ivy hang from them, forming a thick, impassable forest and only the picturesque rocks of the nearby hills show through its greenery.