Mallorca's eastern shoreline between Cala Millor and Porto Cristo conceals a network of sea caves and underwater rock formations that remained inaccessible to most visitors until the 1990s, when transparent-hull catamarans began offering submerged viewing without wet suits or dive certifications. The glass-bottom boat design — a double-hulled vessel with reinforced acrylic panels set flush into the deck — allows passengers to observe posidonia seagrass meadows, gilt-head bream schools, and limestone shelf topography from a seated position while the boat drifts over depths ranging from three to twelve metres. Cala Millor's maritime tourism infrastructure expanded significantly after 2015, when the Balearic Government imposed stricter anchoring regulations to protect posidonia beds designated as UNESCO heritage sites. Operators responded by adopting larger catamarans with stabilised viewing chambers and designated swim zones marked by seasonal buoys. The east coast glass bottom boat trip route now covers a seventeen-kilometre stretch from Cala Millor's Passeig Marítim to the Coves del Drac entrance near Porto Cristo, with most three-hour itineraries including two swim stops at Cala Anguila and Cala Romantica, both sheltered by sandstone cliffs that block prevailing northwesterly winds. The underwater visibility along this coast varies seasonally. June through September typically offers clarity exceeding fifteen metres when morning sea conditions remain calm, while autumn storms stir sediment that reduces transparency to six metres or less. Marine biologists have documented forty-three fish species in the posidonia meadows visible through glass-bottom panels, including Mediterranean parrotfish, octopus, and occasional loggerhead turtles migrating between feeding grounds. Some catamaran tours incorporate cave exploration segments, manoeuvring into partially submerged grottoes where Neolithic pottery fragments were recovered in the 1970s, evidence of Bronze Age seafaring populations who used these natural harbours as seasonal shelters. Booking patterns show eighty per cent of passengers select morning departures between 09:00 and 10:30, when offshore winds remain light and the angle of sunlight penetrates deeper into the water column, enhancing colour saturation of the seabed. The standard adult fare of thirty-two euros includes snorkelling equipment and liability insurance, though onboard lunch service varies by operator — only catamaran sailing adventures with BBQ provisions include grilled proteins and salads in the ticket price.