Piccadilly Lights, W1

In a small room off a corridor in a building on Shaftesbury Avenue, you will find a single old-fashioned light switch. Whatever you do, don't touch it.

It controls 701 square metres of illuminated advertising space that has become one of the most recognised symbols of London around the world. The Coca-Cola sign alone measures 32 metres by 6.6 metres – Britain's biggest permanent curved LED display. It is capable of displaying 16 million colours at 100 frames per second and scalable from 100 to 10,000 pixels wide. The improved TDK display harnesses similar LED technology.

As advertising goes, it's unusually powerful. Research suggests that 34,274,552 pedestrians walk past every year.

Land Securities has owned the site since the 1970s, and it extends to much more than the lights themselves. There's also the small matter of 1,486 square metres of office space, and 6,130 square metres of retail space – spanning 1-17 Shaftesbury Avenue, 1 and 2-6 Sherwood Street and 17, 19 and 20 Denham Street. Retail tenants include Boots, GAP and Barclays, who opened a flagship branch here in 2008.

We haven't told them where the light switch is.