Manhattan-ites must be hard workers. Staying focused when you have a corner office with views of Central Park or the Empire State Building must require some super-human concentration.

But in an obvious effort to reduce distractions, the canny bosses at AT&T built this tower in 1974 that has no windows (more pics).

Designed by John Carl Warnecke, the Long Lines building in New York is a telephone exchange made of pre-cast concrete panels clad with pinkish Swedish granite.

Nearly 170m high, it has only 29 floors - each storey is nearly 5.5m tall.

In true brutalist style, it not only keeps staff focused but is protected from nuclear fallout for up to two weeks after a nuclear blast. Of course!