Open House London returns to the capital this weekend, marking its 21st anniversary by offering visitors the first chance to enter Number 10 Downing Street, the official residence of the UK Prime Minister.

The building's current occupant, David Cameron, hailed the initiative: "Open House London gives people the chance to explore some of London's most unique and celebrated buildings," he said. "As the official residence and office of British prime ministers since 1735, Number 10 Downing Street is a truly historic address. I'm delighted to be opening up the famous black door for the first time this year."

Open House was created in London 21 years ago by Open-City, a leading independent architecture education organisation. The Open House model invites everyone to experience, explore and understand the value of a well-designed built environment. This successful concept has been extended to events in other cities around the world including New York, Dublin & Galway, Tel Aviv & Jerusalem, Barcelona, Rome, Helsinki, Slovenia and Chicago.

Victoria Thornton, Founding Director of Open-City said: "Open House is a unique and vibrant annual event, offering people across London the chance to explore and learn about the capital's architecture. In 2012, 87% of participants said the Open House annual event was the best way see, explore and learn about the capital's architecture. This year we're putting together a great programme of open buildings, walks, tours and talks taking in everything from award-winning contemporary homes to major regeneration areas."

This year, more than 800 buildings, from private residences to world-famous monuments such as Battersea Power Station, will be open to all comers.

For a full list of venues, see the Open House London website.

Scroll down for images of a selection of buildings taking part this year.

City overview
An overview of the City of London Jean-Remi Baudot/openhouselond
Battersea Power Station
The disused power station at Battersea Battersea Power Station/openho
Brixton Windmill
The windmill at Brixton, the closest surviving windmill to central London Reuters
Crossrail works at Liverpool Street
Work on the new subway line Crossrail openhouselondon.org.uk
Cutty Sark
The newly restored Cutty Sark at Greenwich National Maritime Museum/openh
Lloyds building
Detail of the Lloyds of London building Nick Delaney/openhouselondon.o
Middle Temple Hall
Middle Temple Hall openhouselondon.org.uk
NEO Bankside, Southwark
The new face of the south bank of the Thames openhouselondon.org.uk
St Pancras Station
The restored St Pancras station HS1/openhouselondon.org.uk
New York London