Abstract: An aspect of the present invention addresses how to achieve a simple structure, easy and economical to build, that will permit any person, without training or specialized technical equipment, to have direct contact with the underwater environment. In one embodiment, an underwater observation tunnel is provided which operates at ambient pressure, composed of modular sections of a semicircular structure, with transparent molded panels, joined to each other, and with an elevator to transport users from the surface of the water to the operating depth. Air is pumped in a continuous manner through tubes which run along the length of the structure, thus creating an air-filled corridor, where any person can breathe normally, move freely, and observe the underwater environment. The tunnel can be installed and used in any body of water, for purposes of recreational and scientific observation.