Your chance to be top of the town

On the 40th floor of 'The Gherkin', the 360-degree views of London are stunning (Jason Alden)

Welcome to the top of 30 St Mary Axe, or, as it's more affectionately known, the Gherkin. At 180m tall, this shimmering glass monolith, with its distinctive shape and tessellated exterior, is visible on London's skyline for miles around.

Closed off to the public for the rest of the year, the Gherkin threw open its doors to visitors on a first-come-first-served basis yesterday and will do so again today. The weekend marks the 20th anniversary of Open House London, the architectural showcase of the year.

From the top level, 40-storeys high, the 360-degree views are spectacular – weather permitting.

Open House London celebrates the buildings and spaces that Londoners live and work in, affording city-dwellers and visitors alike a rare chance to access, explore and learn about the capital's architecture. This year's theme is "The Changing Face of London", highlighting the evolving nature of the city and the role played by architects and contemporary design in the capital's vibrancy.

More than 750 buildings are participating in the event, which features an array of free activities, including landscape tours, urban jogs and experts' talks.