The pop-up designs changing the city landscape It is now part of the summer, as much as Glastonbury and Henley. Queues form outside rough-at-the-edges constructions, in (mostly) just-arriving areas of (mostly) London, in anticipation of some moment of delight, something that appeals to a love of play or fun or nature. We are invited to be kids or wander in a fragmentary Eden or consume succulent morsels of food or culture, in the middle of - usually - battered tracts of urban landscape. These are pop-ups, temporary constructions intended to enliven public places. They are often the creations of young architects who, their talent and energy outrunning their employment opportunities, initiate, design and build these glimpses of what a better city - more open, more social, more pleasurable, more surprising - might be. Often pop-ups defy economic gravity, relying on unfeasibly large quantities of unpaid enthusiasm and persistence in getting stuff on the cheap. They have the scent of intense hard work and barely averted catastrophe, and the ghostly presence of health-and-safety officers only just placated. They are reminders that, for all its apparent fixity, built space is always in motion, always prone to being readapted and reimagined. At their best they use temporary pleasures to make permanent changes to the way people can inhabit their neighbourhoods. For example, a series of five projects in Union Street, Southwark, of which the forthcoming Lake is the latest, have collectively created the expectation that this harsh location should now be a place of shared public enjoyment. There are reasons to be sceptical about the recent rash of temporary installations. There are pop-up retail outlets that borrow the aura of creative spontaneity to exploit strips of land where they wouldn't otherwise be permitted. Developers use temporary structures and events as marketing tools, and as camouflage for their larger and less charming permanent developments. At best, this can be a case of enlightened self-interest; at worst, a cynical ploy. It should also be noted that, in a parallel universe, the commitment of talented architects might be spent on things like housing, schools or permanent transformations of cities. There is a correlation between the rise of pop-ups on the one hand and, on the other, the rise of very large architectural practices, run on industrial lines, which shape the places where most of us spend most of our lives. Link to video: Sou Fujimoto on the Serpentine pavilion 2013 The Serpentine Gallery in London wouldn't like its annual pavilion, which has been running since 2000, to be called a "pop-up" but, to the extent that it is a temporary constructional event, it is. The Serpentine has brought in an impressive array of international architects over the years but, through no fault of the gallery, its pavilion has acted as a sort of inoculation - by introducing a small quantity of the dangerous bacilli of serious architecture, they prompt the national antibodies to ensure that not too much of it happens anywhere else. Only half the architects honoured by the Serpentine get to build again in this country. There is a danger that something similar could happen to the young enthusiasts behind other temporary structures; that they get confined to a compound for interesting diversions, for Twittertecture, for urbanism in 140 characters. Meanwhile the big boys get to design skyscrapers, whose almost always dismal forecourts show not a trace of the invention or public spirit of those flimsy constructions of boarding and scaffolding poles. But if this spirit could be harnessed more widely -outside London, even - what a wonderful world it would be. THE FLOATING CINEMA Duggan Morris; until 30 September 'A magical idea': the Floating Cinema, designed by Duggan Morris. Photograph: Jack Hobhouse The Floating Cinema was first launched in 2011 but this year has a completely new, purpose-built boat, designed by the architects Duggan Morris. It is a magical idea, to bring together the floating worlds of the cinema with an actual floating boat, and to animate different canalside locations with a touring programme. These include films projected from the boat on to land-based surfaces, viewings inside a small auditorium on the deck, and guided tours of such things as watery crimes, led by a policeman. Of these the least thrilling are probably the on-deck viewings, as you end up in a boxy cabin, which loses the wonder of being on water. But, as a way to activate a lot of city with a small object, the floating cinema is hard to beat. STUDIO IN THE WOODS Studio Weave; open to visit all summer Photograph: Andy Matthews and Jim Stephenson Studio Weave, a young practice led by Maria Smith and Je Ahn, have already become specialists in temporary installations. They designed the first floating cinema and are also responsible for Elmo, the forthcoming artists-studio-on-a-bus. They've also assisted with Studio in the Woods, a five-day workshop (the latest one held last month) in which participants learn to build structures using what is close at hand. Which, in a wood, is wood. Located outside Swindon, the resulting structures can be visited all summer. According to Studio Weave they are something to do with a "slow-living forest people called the Indlekith," but you don't need to let that worry you! DALSTON HOUSE Leandro Erlich (artist); last day on Sunday Link to video: Dalston House: where every visitor becomes Spider-Man In a bashed-up street in Dalston, east London the Argentinian artist has created a full-scale mock-up of the kind of terraced house facade that was there once, complete with mouldings and glimpses of the interior, laid it flat on the ground, and fixed a big mirror over it at 45 degrees. It creates the illusion that you're climbing -or walking - up a vertical surface. It is an invitation to play around with it as you choose, which to judge by the long queues, plenty want to take up. It makes the street into a grown-up playground, where strangers can enjoy clambering around together. Simple, surprising, engaging and brilliant. BOLD TENDENCIES Practice Architecture; until 30 September Photograph: Arcaid Images/Alamy The greatness of Bold Tendencies, now in its seventh edition, is that it takes over a large, underused, existing structure in Peckham, south-east London - an old car park - and makes it into something new. On the roof, with penthouse views of the City of London, is Frank's café, a structure of rough timbers and awnings, while other parts of the building are used for art and music. In a city where space is rationed and priced, it is a luxury to have so much unencumbered, and the car park's size means you don't get the endless queues seen by smaller pop‑ups. Other great pop-ups ROAMING MARKET Aberrant Architecture; touring A blue double-decker market stall (pictured above) that can host chess, fortune-telling and other events, touring the neighbourhood of Waterloo station. THE LAKE Exyzt; coming soon The Lake, situated on a strip between railway arches and a council estate in Union Street, Southwark, is "a place to go on holiday in your own city." Boating, paddling and sunbathing will be offered amid a blue-and-white scheme intended to evoke a Greek island village. MOBILE ORCHARD Atmos; tour over, but available for community hire from treesforcities.org "An inhabitable hymn to the mobile fruit tree" - manmade structures that you can sit in, with a supply of apples grown elsewhere. A monster development of apartments and suchlike is finally going to rescue London's largest ruin. While we're waiting, part of the grassland becomes the venue for fitness sessions, a garden festival and other events. ELMO (BUS) Studio Weave; launched on 3 August with a year-long programme A handsome old Bedford bus, once a mobile library, will become a roving artist's studio in east London. Visiting parks and other public places, it will enable the public to take part in workshops and try out artistic skills. Climbing-frame-as-art. One of the best in the Serpentine's series.