30 St Mary Axe

The Fifth HQ.
30 St Mary Axe is a skyscraper in London's main financial district, the City of London. It is widely known by the nickname "The Gherkin", and occasionally as a variant on The Swiss Re Tower, after its previous owner and principal occupier. It is 180 metres (591 ft) tall, making it the second-tallest building in the City of London, after Tower 42, and the sixth-tallest in London as a whole. The building's name is its address — St Mary Axe being the street it is on.

It is the secret home to The Fifth and houses vast research stations and hundreds of staff