Juan Muñoz: Double Bind, installation shots; photo is stored here .

By far the largest enclosed gallery in London, the Turbine Hall at Tate Modern is an unforgiving and difficult place to exhibit work. In June, following on from Louise Bourgeoise's inaugural and highly successful installation, Tate Modern unveiled the second commission in its Unilever series. Approaching the problem of installation and the enormity of space head on, Spanish artist Juan Muñoz installed Double Bind (2001), a work that is both monumental and yet understated. A false floor has been erected that splits the Turbine Hall in two, and two elevators effortlessly glide from the now concealed basement area up to the glass roof 300 feet above.

Painted an institutional grey colour, this floor is in keeping with it surroundings and easily overlooked; whilst the elevators, with their stainless-steel veneer and riveted supports, are almost camouflaged by the industrial power-station surroundings of Tate Modern itself. And this is where Double Bind is at its most successful: in electing to incorporate - that is to say, the building into the work, Muñoz effectively questions the conventional structures and demarcations that exist between the work and the space it occupies.

Descending into the underground car-park-like zone beneath the artificial floor, this visual ambiguity becomes more acute and unsettling: vertical supports, painted in the same colour as the Turbine Hall, bolster the floor and two enclosed steel cages contain the mechanics necessary to keep the elevators in motion. Underlining the intimate understanding between work and space, the deep hum from the Tate's turbines, which still produce electricity, conspires with the metallic grating of the hawsers supporting and driving the elevators. Having visited the work many times, twice with a group of contemporary art students, I was interested to hear that a considerable number of them had entirely overlooked the underground part of the work upon first entering the building. Given the immense and substantial size of the work, this sounds preposterous until you realise how Double Bind acts as something of a conduit for the realignment of the surrounding space. Standing there in the murky gloom, there is a sense of Double Bind expanding and drawing in all that exists around it: sections of the Tate - including the long brushed concrete entrance ramp, the Nissen hut-like cloakroom, and the underbelly of the stairs leading to the bridge, even the fire-extinguishers and heating vents - all start to retrospectively amalgamate with the work and make it increasingly difficult to conclude where the Tate starts and the work finishes.

The most dramatic part of the work, moreover, is concealed insofar as what first appeared to be the floor is in fact a crawl-space of sorts inhabited by almost life-size characters, all of them identical, and all performing vague, possibly futile activities. What is left unclear, however, is what role these figures perform, if any, in the 'mise en scene' of the work. Are they subterranean workers insuring that the lifts continue their route? Or are they caught in a limbo reminiscent of Dante's Purgatory with a circumstantial Heaven hovering above them in the form of two transcending elevators ? These characters, with their half-wince, half-smile expressions, were modelled on Muñoz's own brother and encourage the viewer to narrativise the tableau before them. Muñoz's art, and Double Bind in particular, is very much the art of narrational ambiguity and spatial contingency, an installational gambit that relies upon the confident and complex interplay of space, place and memory that the artist draws upon throughout his work.

Dan Flavin: untitled (to the real Dan Hill) 1b, 1978, blue, green, pink, yellow fluorescent light, 244 cm high; image held here .

Across town, the Serpentine Gallery have dealt with the exigencies of installation with similar success. Since its refurbishment a few years back, the Serpentine has been struggling to fully realise the potential of its idiosyncratic space; it has, nonetheless, achieved this with an impressive installation of Dan Flavin's neon-light filled work. The redolent memories that converge around neon light - small-town American bars, the expectant lights of casino towns, and the alienated urban diners of Edward Hopper's paintings - provide these works with a ready-made memory-bank. Installed in the Serpentine, these works bring all of that with them and present not only a memory of elsewhere but an enquiry into the here and now. If, for example, you take a clock-wise route through the space, you are confronted with the striking Untitled ( To you Heine with admiration and affection),1973, a series of gridded green neon-tubes that stretch the whole length of the gallery space, some ten metres in all. This piece, literally, colours your view of the rest of the show: turn right, for example, into the middle gallery and the usually white neon tubing of Flavin's Tatlin series ( dating from the 60s and 70s) is now an ethereal red colour as the after-image of the previous work shifts your colour perception. If, however, you choose to go anti-clockwise, as I did on my first visit, the white tubing is just that, a ghostly and yet very substantial white. Whilst Muñoz's Double Bind might be described as a work of two halves, Flavin's is a show of two possible routes - both of them worth taking.

It would seem that the problematic of installation could provide something of a theme for a number of other shows in London. On the South Bank, the Public Arts Development Trust have commissioned a film from Pipilotti Rist, The Belly Button Like a Village Square, 2001, and projected it onto the bunker that stands sentry to the right of the National Theatre. Whilst the surrounding South Bank area has been much derided in the past, this bunker is one of its better facets: inaccessibly flat, functional and resolutely square, it makes for an ideal surface upon which to project a film. Rist's work, in turn, occupies an uneasy ground between pop-video and arthouse film: lilting vocals accompany a series of haunting images that depict, mostly to good effect, women performing unfamiliar and remotely disturbing tasks. From Waterloo Bridge, heading south on the 171 bus, the work looks extraordinary, less abstracted than when you stand in front of it and big enough to be clearly visible for miles around. And it is this aspect of the work, to a certain extent, that illustrates what each of the above works manage to achieve: the successful and provocative use of what might be otherwise considered the restrictions of a place or a space on an installation-based work.

Juan Muñoz: Double Bind , Tate Modern, June 200-March 2002
Pipilotti Rist: The Belly Button Like a Village Square , National Theatre, September
Dan Flavin: Serpentine Gallery, August/September

Anthony Downey lectures at Goldsmiths College and Sotheby's Institute in London.