Running from Friday 18 September to Sunday 20 September, Open House London gives people who live and work in the capital a rare opportunity to take a glimpse at some of London's most iconic buildings from the inside.
This year more than 700 buildings are opening their doors, and as with previous years there's a huge variety on offer from beautifully designed residences to innovative infrastructure projects and major landmarks. There's also the opportunity to take part in a programme of walks, tours, cycle rides and expert talks (and yes, we double-checked, London really is supposed to be dry and relatively warm this weekend).
Here are some of the best features of Open House Weekend 2015
The Gherkin, the City
Love it or hate it, 30 St Mary Axe has become one of London's most iconic buildings and certainly dominates the skyline - but what's it like inside? Groups of up to 30 people will be allowed in every 10 minutes, for a maximum of 20 minutes at a time.
Special information: This is a high security building with bag and body scans. Photo ID is required.
10 Downing Street, Westminster
David Cameron's current pied-a-terre and the London residence of Prime Ministers back as far as 1735, who wouldn't want a glimpse at the UK's seat of power.
Special information: This is of course a popular destination, so tickets are by ballot only. Photo ID is required.
Crossrail sites, various
London's major infrastructure project is opening up yet again, with opportunities to see the work that is taking place beneath our feet at various sites including Liverpool Street and Farringdon.
Special information: This is an active construction site, so there is no access for wheelchairs and pushchairs and no toilets. The hourly tours must be pre-booked.
The Gap House, Bayswater
Here are City A.M. we have something of an obsession with skinny homes and this "super-eco" home claims to be London's skinniest. At just eight foot wide, it sits between two listed buildings and uses ground source heat pump heating and harvests rain water.
Special information: As a family home, this is only open on Sunday between 10am and 12pm
The Gingerbread House, Hackney
This is an award-winning new build on the site of a former box factory. It will be top of the list for architecture fans, but you have to pre-book for tours.
Maggie’s Culture Crawl
This moonlit walk through London gives culture vultures the opportunity to fill their boots and raise money for Maggie's Cancer Centres at the same time.
Special information: This is a 15-mile walk overnight, so it's not for the faint-hearted, but you will get exclusive access to some of London's best-loved buildings and food and drink along the way, as well as some entertainment. It costs £40 to register, which you can do on the day, and Maggie's also asks that you raise £200 for the charity.
City A.M. is taking part in Maggie's Culture Crawl London this evening. Help us in our quest to raise £1m for a Maggie's Centre at St Barts.