Fornells guards a natural harbour nearly four kilometres long that rarely exceeds five metres in depth. That geometry — deep enough for keels, shallow enough to stay calm under the tramuntana — made the inlet the safest anchorage on Menorca's exposed north coast. Boat hire fornells tours still cast off from the same waterline the fishing fleet has used for four centuries, along Passeig Marítim. Fortification came first. The Castell de Sant Antoni rose at the harbour mouth in 1625, survived the British and French occupations of the eighteenth century, and was demolished on Spanish orders in 1782. Its foundations are still legible from the water. Two decades later the returning British raised the Torre de Fornells above the entrance, finished in 1802 and still the largest defensive tower on the island. West of it, at Sanitja, the Roman port of Sanisera served the fleet that arrived with Quintus Caecilius Metellus in 123 BC. The Cap de Cavalleria lighthouse, lit in 1857, stands above those excavations at Menorca's northernmost point. The village never industrialised. Fewer than six hundred people live here year-round. Lobster fishing sustained the community into the twentieth century, and the fleet's low wooden llaüts set the template for the skippered craft working this coast today. UNESCO designated the whole island a Biosphere Reserve in 1993, and the s'Albufera des Grau natural park now protects the wetlands and headlands east of the harbour. Building along the shoreline is capped, and several of the coves reached on Menorca north coast sailing trips have no road access at all. That is the north coast's peculiarity. Its cliffs run to dark slate and red ferruginous clay, older and rougher than the pale limestone of the south, and they weather into beaches the colour of rust: Cala Tirant, Cavalleria, Pregonda. Posidonia meadows below hold the water to a clarity that makes the sandbanks legible from the surface, and Fornells boat rental skippers read those beds as navigation marks. Reaching the western coves means rounding Illa des Porros and the wind-scoured headland at Cavalleria, a run of roughly nine nautical miles. Boat hire fornells tickets are, in practice, admission to a coastline the island's roads never reached.