Open House takes public behind the capital's green doors

The annual event gives curious visitors the chance to peek inside some of London's most celebrated or unusual private properties.

Nearly 700 buildings are taking part this year, including Lloyd's of London, the Bank of England, the Foreign Office, a rooftop nursery in Hackney and the Hurlingham Club in Fulham.

Many are never normally open to the public and others will allow unprecedented behind-the-scenes access for the weekend. Every borough is involved.

The theme of this year's event on 20 and 21 September is sustainability and more than 100 of the buildings have an environmental aspect.

There will be guided walks including tours of the Olympic Park and Barking Riverside, which is one of the largest brownfield sites in Europe and is to have 10,800 homes plus a school and nature reserve built on it as part of the Thames Gateway development.

Julie Leonard from Open House said: "It's just a wasteland beside the A13 at the moment but it will become a whole new part of London. They are recycling building materials there that are shipped up the Thames from all over the UK."

There are also talks and family events including the chance to create a giant cityscape at the University of Westminster. Architects and a graffiti artist will be on hand to help turn inspiration into reality.

Other highlights this year include:

A rare chance to see the bells and belfries at St Botolph's Church in Aldgate, EC3. The 1744 church, designed by the architect of Mansion House, also houses London's oldest organ.

10 Queen Street Place, EC4, a recently built office by the Thames with a roof garden and three atriums linked by bridges.

Kensington Roof Gardens, above the old Thirties Derry & Toms department store in Kensington High Street.

Trellick Tower, the monumental Seventies social housing block which looms over Notting Hill and has become one of London's most desirable addresses.

The Great Barn at Harmondsworth, a 15th-century tithe barn which is threatened by the expansion of Heathrow.

19 Hanover Square, a refitted Seventies office building which uses natural light, bamboo panelling and the original concrete structure to cool the building.

Eco House in Monmouth Road, W2, a family home on a tiny site which has a carbon footprint as minimal as its actual footprint.

Westminster Academy, a colourful new school in Harrow Road, W2, which was named London Building of the Year 2008 by the Royal Institute of British Architects. It has a dramatic glazed atrium.