Below roughly 150 metres, the Black Sea does not breathe. Hydrogen sulphide fills more than eighty percent of its volume, making it the largest body of oxygen-free water on the planet. Life crowds into the thin, brackish upper layer — the same sunlit band that VIP Catamaran Cruise Sunny Beach tours cross each summer between Nessebar Port and the headlands of Burgas Bay. Salinity here sits near 17 parts per thousand, roughly half that of the Mediterranean. The water reads greener, softer, almost freshwater-pale against a white hull. The port they leave from is older than most European capitals. Thracians settled the rocky peninsula as Menebria; Dorian Greeks refounded it around 510 BC as Mesambria, and the city minted its own silver coinage within a century. Rome absorbed it, Byzantium fortified it, and Bulgarian and Byzantine rulers traded it back and forth for four hundred years. Roughly forty churches once stood on a peninsula measuring about 850 metres by 350 metres. Around a dozen survive, including the eleventh-century Old Metropolitan of St Sophia and the fourteenth-century Church of Christ Pantocrator, whose facades alternate brick, stone and green ceramic rosettes. UNESCO inscribed the Ancient City of Nessebar in 1983. Three kilometres north, the shoreline changes register entirely. Sunny Beach — Slanchev Bryag — was laid out from empty dunes in 1958 as a state resort, and now runs roughly eight kilometres of sand backed by hotels. Beyond it, Sveti Vlas shelters one of the largest yacht marinas on the Bulgarian coast beneath the last ridges of the Stara Planina. Those mountains meet the water at Cape Emine, the point that divides the northern and southern Black Sea littoral. Catamaran routes along this coast read as a compressed geography lesson: Roman peninsula, socialist-era resort, alpine foothills, open sea. The vessels themselves are a recent arrival. Multihulls entered Black Sea leisure fleets seriously only in the 2000s, after Bulgaria's marinas were rebuilt for private ownership; before that, the coast belonged to hydrofoils and trade-union steamers. A catamaran's two slender hulls carry a wide deck with little roll, which suits a sea that has no meaningful tide and, in July and August, long flat mornings. That stability is the quiet argument behind every VIP Catamaran Cruise Sunny Beach tour: a steady platform for looking at a shoreline that has been looked at for 2,500 years. Sailing time from Nessebar Port to the Emine headland and back is measured in hours; the history it passes is measured in millennia.