In 2009, a single cast-concrete figure was lowered onto the sand flats off Manchones Reef. More than 500 followed within three years. The Museo Subacuático de Arte — MUSA to the dive boats that moor above it — sits in four to eight metres of water, and it is the chief reason first-time divers who discover scuba diving isla mujeres come back describing sculpture rather than fish. Each piece was cast from pH-neutral marine cement, textured to recruit coral polyps and to pull traffic away from the living reef alongside it. The island is small: roughly seven kilometres from Punta Norte to Punta Sur, and barely 650 metres across at its narrowest. Its western shelf drops gently into the Mesoamerican Barrier Reef, the second-largest reef system on earth. Spanish navigators recorded the island in 1517 and named it for the clay figurines of Ixchel found on the southern headland. Since 1996 the surrounding water has been federally protected as the Parque Nacional Costa Occidental de Isla Mujeres, Punta Cancún y Punta Nizuc, and the 7 USD National park conservation fee, per person, is collected on that authority. Manchones Reef runs for close to a kilometre south-east of the island, its coral heads topping out around ten metres. The current is modest, the bottom is sand rather than rubble, and the profile rarely exceeds twelve metres — the reason instructor-led discover scuba diving isla mujeres tours are run here for divers holding no certification at all. Local boat manifests still list the same outing simply as buceo en Isla Mujeres. El Farito, the shallow reef beneath the old lighthouse marker on the lee side, sits shallower still, around five to eight metres, and carries schooling sergeant majors, French angelfish and the occasional southern stingray buried flat in the sand. What the water holds now is partly engineered and partly inherited. Brain and elkhorn coral have colonised the older MUSA figures; parrotfish graze them; barracuda hang above the deeper installations in the slack hour after dawn. Whale sharks pass offshore between mid-May and mid-September, a separate undertaking entirely. Demand for discover scuba diving isla mujeres tickets has climbed with the museum's reputation, and the island's fleet now works a schedule built around morning light, when the shelf is clear and legible even to an untrained eye. An Isla Mujeres reef diving tour is, in the end, a visit to a gallery that is still being built by its own tenants.