The central station on Stockholm’s underground forms the hub of the city's public transport system. It has been upgraded in recent years to allow the hundreds of thousands of commuters who use it every day to move quickly between the three metro lines, the railway station and the bus terminal.

The pedestrian zone that connects the different terminals looks like the inside of a natural cave. The grey of the living rock is picked up both in the floor and in the large, circular steel structure suspended from the ceiling, which houses, recessed inside it, twenty-four projectors in an anthracite finish. The lighting design, by WSP, called for a colour temperature of 4000K and wide, 64° optics for the projectors, to open up the underground passageway and give the impression of greater space.

Elsewhere, the ceiling in the corridor that leads to the blue line of the Stockholm underground system, which also has the natural look of excavated rock, houses projectors (4000K, 2W, 64°) in a white finish, pointing perpendicularly at the ground.