Menorca's limestone coastline erodes at roughly two millimeters per year, carving the island's 216 kilometers of shoreline into slot canyons, sea caves, and submerged arches invisible from land. Glass bottom boat tours departing from Ciutadella's historic port exploit this geology, using transparent acrylic hulls to reveal underwater formations without requiring passengers to dive or snorkel. The technology dates to the 1870s, when English inventor Samuel Baker patented viewing boxes for shallow reefs, but modern marine-grade polymers now allow boats to operate in depths exceeding fifteen meters while maintaining optical clarity. Ciutadella's western position grants access to Menorca's least-developed coast. Departures from the Port of Ciutadella track south toward Cala en Turqueta and Macarella, where Posidonia oceanica seagrass beds—protected under the Natura 2000 network since 1995—host grouper, octopus, and schools of salema porgy. The seagrass meadows filter an estimated 1.2 million liters of seawater per hectare daily, maintaining the transparency that makes glass bottom viewing viable. Tour operators favor morning slots when sunlight penetrates to the seabed, illuminating rock strata laid down during the Miocene epoch twenty million years ago. The boats themselves vary by operator. Catamarans offer stability in open water, essential for viewing during moderate swells, while smaller monohulls access narrower coves. Most vessels carry fifteen to thirty passengers, with the transparent section occupying the central third of the hull. Hydrophones installed on some boats broadcast the clicks and whistles of bottlenose dolphins, common in these waters from May through October. Ciutadella's marine traffic ordinances restrict boat speeds within two hundred meters of shore, ensuring minimal disturbance to nesting seabirds on the coastal cliffs. Glass bottom boat Menorca Ciutadella tours typically last ninety minutes to two hours, with longer excursions incorporating swimming stops at roadless beaches. The port's north-facing marina protects departures from the Tramuntana wind, though operators cancel trips when wave height exceeds one meter. No prior experience is required, and the viewing experience suits all mobility levels, as passengers remain seated throughout. Ciutadella's position fourteen kilometers from the open Mediterranean means calmer conditions than departure points on Menorca's northern coast.