The Monument to the Great Fire of London
The Great Fire of 1666 was one of the worst disasters to ever strike London.
A 61 metre column was therefore constructed to mark the point where the Fire started - the King's baker's shop on Pudding Lane.
The Monument was designed by Sir Christopher Wren and Robert Hooke between 1671 and 1677. At the time it was the tallest free-standing column in the world. It also contains a 311 step spiral staircase to provide a panoramic viewpoint to the people of London, making it the 'London Eye' of the 17th century!
However, the designers decided to provide a double use for this tourist attraction and decided to place a central shaft inside it to use a zenith telescope for gravity and pendulum experiements. The shaft lead down to an underground laboratory underneath the column. Each step leading down to the lab is apparently exactly six inches high to allow for accurate reading of barometric pressure.