The Gallarus Oratory is the only completely preserved cantilever vault building on the island that was built using drywall technology and has a rectangular floor plan. The walls, which are more than one meter thick, arch over an interior space of just 3 by 4.50 meters with two openings: the western door and the eastern window.
At the same time, the prayer house is an excellent example of the architecture of that time. Because the stone layers, which are held together almost without mortar, are so carefully layered on top of one another that they drain the water to the outside so that the chamber remains dry.