The secret places to poke around while you briefly have the chance this autumn.

There is something of the forbidden fruit about Open House London. Founded in 1992, this annual festival aims to encourage greater engagement with the architecture of Britain’s capital, but its finest pleasures are those of the voyeur. Prising the doors ajar to some 800 buildings across the city, Open House lets you into spaces typically kept behind lock and key. From Tudor manors and Victorian pump-houses, through to Georgian terraces, modernist apartment blocks and contemporary maker spaces, Open House invites you to peek behind the curtain wall. Here’s a selection of five highlights from this year’s line-up of secret spaces.

Messrs GR Yeats and Eric Bedford, Ministry of Public Buildings & Works (1965)

A structure studded with enough aerials to handle 50,000 telephone calls and 40 television channels, the BT Tower has had a lamentably chequered history since opening in 1965 as the Post Office Tower. What had originally intended to be a public space – complete with its Space Needle-esque revolving Top of the Tower restaurant on the 34rd floor – was eventually forced to close in 1981 following a decade of security risks after an IRA bombing in 1971. Fortunately, however, the building escaped the fate reserved for it in Mr James Herbert’s gloriously atrocious 1975 pulp horror novel The Fog, in which it was demolished by a Boeing 747 piloted by a captain intoxicated with rage (by the book’s titular fog, of course). A chance to get back inside and explore its various crannies and storeys is not to be sniffed at.

45 Maple Street, W1T 4BG

Assemble (2014)

If ever a space were to represent a contemporary grassroots approach to architecture, it is the Blackhorse Workshop in Walthamstow. Created by the Turner Prize-winning architecture collective Assemble, the workshop is a building that aims to democratise design, taking power out of the hands of the starchitects and instead placing it into those of the community of makers that call it home. Equipped with saws, planers, drills and lathes, the Blackhorse Workshop opens architecture up the public, inviting visitors to engage with the joy of making. Visiting during Open House is a chance to see one of the world’s most progressive architecture practices in action, and a justification as to why the Turner jury risked the ire of the art world in bestowing one of its most prestigious awards upon a collection of socially minded architects.

1-2 Sutherland Road Path, E17 6BX

Sir Giles Gilbert Scott (1935)

How times change. When it opened in the 1930s, Battersea Power Station was a redbrick paean to the decade’s belief in industrial progress, yet by the 1970s, the gloss had somewhat worn off. As running costs rose, the plant’s operations were gradually wound down, with the entire site eventually becoming mired in a tedious game of back and forth in which developers, theme parks and, bizarrely, Chelsea Football Club competed to take over the site. The station is now scheduled to be converted into offices for the omnivorous Apple corporation. God bless Open House, then, for providing a chance for guests to prowl the former power station’s Art Deco balconies and fluted columns before it closes down for a lengthy process of renovations, restoration and conversion.

Grosvenor Arch, SW8 4NN

Mr Richard Gough (1698)

In a city obsessed by blue plaques, Open House does a neat line in catering to a paparazzi-like desire to see how the great and the good live – at least for those curious about the celebrities of the 18th century. Chief among these historical delights is the timber-framed, brick townhouse in which the polymath Mr Samuel Johnson assembled his A Dictionary Of The English Language, the good doctor’s titanic work of lexicographical scholarship. A reminder that the pleasures of architecture are often to be found in how a space is used, and the events that have transpired behind closed doors, Dr Johnson’s small space stands as something of a totem for the Open House festival. In the words of its one-time resident, “When a man is tired of London, he is tired of life.”

17 Gough Square, EC4A 3DE

Sir Denys Lasdun (1964)

Less well known than his pioneering work on the Royal National Theatre on the South Bank, Sir Denys Lasdun’s Royal College of Physicians building – nestled on the Outer Circle of Regent’s Park – is nonetheless a delight. Covered in white mosaic, the building sits proudly on pilotis (essentially, stilt-like columns) that prop it up among the verdure of the parkland. Meanwhile an interior “Moving Wall” allows the space to be variously divided or opened up by means of a clever hydraulic system. It all amounts to a pleasingly ambitious building, central to which is a ceremonial marble staircase that has enough sense of drama and showmanship about it to have served admirably as the catwalk for Paul Smith’s AW16 womenswear collection.

11 St Andrew’s Place, Regents Park, NW1 4LE