UltraSwim 33.3 Bay of Kotor

At the entrance to the Bay of Kotor, sheer limestone cliffs plunge straight into the Adriatic Sea. This dramatic coastal arena in Herceg Novi, Montenegro, sets the stage for #21MONTENEGRO, an endurance open water swimming event that bridges open maritime passages and sheltered fiord-like channels. Swimmers take to these storied waters organized by UltraSwim 33.3, facing either the signature marathon distance of 33.3 kilometers or a half-distance route of 16.65 kilometers. The route traces the rugged contours of the Luštica peninsula, navigating the shifting boundary between the open swell of the Adriatic and the calmer embrace of the inner gulf. Swimmers launch their journey from a start line set inside a vast blue sea cave, gliding through illuminated waters before circumnavigating the perimeter of the fortress island of Mamula.

The course steers into maritime history with swims passing through abandoned Cold War submarine pens carved into the shoreline cliffs, and features an ambitious cross-border passage leading from Croatia back into Montenegrin waters. Held in early October, the event benefits from comfortable, lingering autumn warmth across the bay, offering mild sea temperatures that make long-distance marathon sets accessible without the bite of summer heat.

The Bay of Kotor: drowned river valleys and limestone cliffs

The striking setting of the Bay of Kotor is not a true glacial fiord, but an ancient ria formed by the gradual tectonic drowning and karstification of the ancestral Bokelj river system. Towering limestone massifs rise immediately from the shoreline, framing an enclosed basin that holds an average depth of around twenty-seven meters, descending to sixty meters in its deepest channels. As water moves inward from the sea, the gulf compresses drastically at the Verige Strait, a narrow sea gate only 340 meters wide. This drowned karst landscape remains dynamically connected to subterranean waterways that surge beneath the mountains. Following heavy mountain rains, subterranean flows erupt into coastal springs like Sopot, which surges from a high cave to send a roaring twenty-meter waterfall straight into the sea, churning the saltwater surface into white froth. Nearby cavern systems, such as the Spila cave, discharge winter rivers directly from the limestone rock face, constantly refreshing the bay with sweet underground mountain runoffs.

Mamula Island and the fortresses guarding the sea gate

Standing guard right at the entrance of the gulf between the Prevlaka and Luštica peninsulas lies Mamula, a circular islet measuring just two hundred meters in diameter that was known to Venetian sailors as Rondina. Built in 1853 under Austrian General Lazar Mamula, an imposing stone fortress sprawls across ninety percent of the island's rocky surface. Designed as a strategic stronghold alongside complementary batteries at Cape Oštro and Cape Arza, the outpost was built to seal the maritime mouth of Kotor against invading fleets. Directly across the sound on the northern mainland shore, the historic town of Herceg Novi anchors the entrance to the bay. Founded in 1382 by King Tvrtko I of Bosnia on the footprint of an ancient fishing settlement, the citadel grew under successive Mediterranean powers, including Spanish forces who erected the elevated Hispaniola fort during their brief presence between 1538 and 1539.

The passage saw heavy naval combat in June 1539 when an Ottoman fleet of thirty galleys blockaded the strait, leading to nearly a century and a half of Ottoman rule until Venetian commander Girolamo Cornaro retook the port in 1687.

Our Lady of the Rocks and the sacred waters of Boka

Venturing deeper into the inner bay reveals an extraordinary monument of seafaring devotion at Our Lady of the Rocks. Unlike the natural terrain surrounding it, this sanctuary is an artificial island built by sinking seized and scuttled ships laden with heavy rocks. The work began after local mariners discovered an icon of the Virgin Mary upon the rock on July 22, 1452, establishing a spiritual beacon in the center of the water. That connection between mariners and the sea persists today during the annual fašinada on July 22, when bay residents cast stones into the sea and reinforce the island foundation. The island is capped by a navigational light at its northern tip.

Herceg Novi and the Pet Danica coastal promenade

Back on the coastal rim of Herceg Novi, the Pet Danica promenade stretches for seven flat kilometers along the waterfront, linking Meljine to Igalo. The path serves as the social heartbeat of the shoreline, where swimmers and locals stroll, dine at waterside taverns, and slip into the sea. Rising behind the water is the tiered village known as the city of steps, where steep stone staircases wind. A south-facing exposure against warming limestone bluffs grants Herceg Novi an exceptionally sheltered microclimate, fostering a swimming season that stretches across five months of the year. At Igalo, natural mineral springs and therapeutic sea mud offer an effortless natural ritual for tired muscles after hours of open water swimming.