Glass brick, also known as glass block, is an architectural element used in areas where privacy or visual obscuration is desired while admitting light, such as underground parking garages, washrooms, and municipal swimming baths. Glass block was originally developed in the early 1900s to provide natural light in industrial factories.
Electrical circuits such as lights can be isolated by placing them in a very small room or passageway outside the area being illuminated, such that no electrical leakage is possible. This also helps prevent vandalism and theft of bulbs, or removal of bulbs (e.g. to perpetrate crime.)
Some washrooms such as those in Dundas Square, Toronto, Ontario, Canada, have glassbrick windows that run all the way around the washroom, to create an illusion of natural light from all directions. This requires small passageways that run all the way around the outside of the room, for servicing the light sources.