Mark 21-22 September 2019 in your diary: it's your annual chance to poke around some of the capital's most interesting buildings with Open House London. All for free.
Over 800 buildings will take part in this year's festival. Some require pre-booked tickets (free), or a ticket allocated by ballot, but for the majority you can just turn up and explore.
Prebook for these buildings
The programme contains dozens of pre-book options. Here are just a few that caught our eye.
Abbey Mills Pumping Station: Glorious sewage-pumping facility designed by Joseph Bazalgette, near Stratford. Prebook, no ballot.
Australia House: The huge Portland stone diplomatic mission on Strand. Prebook, no ballot.
55 Broadway: One of the last chances to look around London Underground's art deco HQ above St James's Park station before it's redeveloped. Prebook, no ballot.
Dulwich College: Posh school with both modern and historic buildings. Prebook, no ballot.
The Old Bailey: Take a tour of the Central Criminal Court, and see if they'll take you downstairs to see the Roman remains. Prebook, no ballot.
One Canada Square: Head up to the 39th floor of the pyramid-topped tower at Canary Wharf.
10 Downing Street: See the rooms from which the country is (theoretically) ran. Ticket by ballot.
The Reform Club: See the Pall Mall club from which Phileas Fogg began his 80-day trek around the world. Ticket by ballot.
ROOM by Antony Gormley: Climb inside a 'giant cuboid crouching figure based on the artist's body' at Mayfair's Beaumont Hotel. Not something you get asked to do every day. Prebook, no ballot.
St Pancras Chambers and Clock Tower: The marvellous hotel complex in front of St Pancras station. Prebook, no ballot.
Other highlights that don't need a ticket
Just turn up on the day to look round these buildings. The full list runs into the high hundreds, so we've selected a few that we've enjoyed on previous Open House weekends.
15 and a half Consort Road: A private address in Peckham with a retractable roof.
BAPS Shri Swaminarayan Madir: Huge Hindu temple near Neasden.
Becontree Estate bus tour: Something a bit different.
Crystal Palace subway: London's most beautiful underpass, surely.
Foreign and Commonwealth Office: A perennial favourite in Open House — everyone should see it at least once.
Isokon Building: Modernist housing up near Hampstead.
Lloyds Register Group: Not the more famous Lloyd's Building, but an office of two halves (historic and modern), round the corner on Fenchurch Street.
London School of Hygiene and Tropical Medicine: The large college with pictures of insects and pests on its facade, close to Senate House. Has a striking, modern interior.
Lovekyn Chapel: Kingston's got a very rare 14th century survival that not many non-locals know about.
Masonic Temple: Andaz Liverpool Street: Bizarre survival hidden inside modern hotel.
One Bishops Square: Unlovable bland office building in Spitalfields, but has a lovely roof garden.
Royal College of Physicians: Grade I-listed concrete hulk to the south-east of Regent's Park.
Royal Courts of Justice: Landmark building on Strand. Definitely one to try if you've never had the pleasure.
Royal Hospital Chelsea: Another grand building that everyone should explore at some point.
Salters' Hall: Lots of livery halls are open to the public this weekend, but this one offers something a little different, with its brutalist architecture and freshly landscaped surroundings.
Smithfield Meat Market: The large Victorian complex's days as a butchery are numbered, so see it now before its historic purpose changes forever. Also, the Poultry Market has one of London's top 6 truncated hyperbolic paraboloid roofs.
Unilever House: the big curvy building at the north of Blackfriars Bridge has an astounding interior.
Open House London 2019 runs 21-22 September. Entrance to all buildings is free. A printed programme costs £8.50.