The boat rocks once, a warm wind pressing the ocean flat, and then you crouch under a glass-fronted helmet and step down into a light that feels like suspended air. The seabed opens in grays and ochres; fish thread between volcanic boulders while bubbles climb the hose to the surface. Sea Trek puts a panoramic helmet over your shoulders and feeds air from a small surface boat so you can walk on the seabed — breathing normally, feet on real sand, the current occasionally nudging you like a curious companion.