Where: Cleveland Street, W1 (Formerly the post office tower and the british telecom tower or bt tower)

What: One of london's most famous landmarks, the telecom tower (originally the post office tower) was opened on the 8th October 1965. It stands at an impressive 620 ft. (or 188 metres). With 34 floors, it was built from 13,000 tonnes of concrete, steel and glass at a cost £2 million.

Telecom tower was built to allow the transfer of telephone signals without interference from other tall buildings.It was the tallest building in London for 15 years, before being overtaken by the NatWest Tower in 1981 (and then docklands). For many years it was open to the public, offering fantastic views of London from the revolving restaurant near the top.

In the early hours of October 31 1971 a bomb exploded on the 31st floor (for which no one has ever claimed claimed responsibility). Although no-one was injured, the physical damage took two years to repair. Then, in 1980, the tower was closed to the public for repairs to the elevators, and it never reopened. By this time more than 4.5 million people had visited it.

Why is it round? The architects that designed it wanted it to be able to survive a nuclear attack (so that the british government would still be able to communicate with the world, post bomb). They noted that the only buildings that survived in Hiroshima and Nagasaki were circular, allowing the enormous blast wave to surge round them, so they built it round.

Want to know a secret? Despite the being one of most recognisable and conspicuous landmarks in London, telecom tower was classed as an 'official secret' for almost 30 years. Taking or possessing photos of it was technically an breach of the Official Secrets Act and the tower was even omitted from all Ordnance Survey maps until the mid 1990's.

How fast does the restaurant rotate? The 34th floor used to host a Butlins-leased restaurant (yes that Butlins), built on a 3-metre wide revolving segment. The restaurant spins through 360º every 22 minutes (or at a speed of 0.17 km/h).

The restaurant floor is now used for corporate events but, sadly, the general public are not admitted.

Nearest underground station: Warren Street or Goodge Street