Restrained exhibitionism: in urbane European cities, Rem Koolhaas is the most bad-mannered boy on the block. But he ripostes to the world's capital of kitsch with minimalism, and elegance.

When the Russian-born theatre designer Theodore Komisarjevsky borrowed from Venice in creating the interior of the Tooting Granada -- a super-cinema of 1931, now relegated to use as a bingo hall -- he did it with bravura, inventing as much as he copied. By contrast, the Venetian Hotel in Las Vegas merely mimics: its version of La Serenissima is pinched yet bombastic, blowsy and vapid, from the vast porte-cochere to a canal that's as grand as a drainage ditch. You look, you shudder, you know what is to come. There are no surprises -- until you turn into a vaulted concourse that's expensively frescoed, gilded, and marbled in a style best described as Reader's Digest Renaissance. Beneath one of the porticoes is a wall of CorTen steel plates that casual tourists may mistake for a construction fence concealing new boutiques. Look closer: the giant silk-screened letters spell out 'Guggenheim Hermitage', signalling the association of Russia's greatest art museum with Thomas Krens's burgeoning empire.

Equally surprising is the refinement of this 760 sq m insertion. In the past, Rem Koolhaas has been all sharp elbows and abrasive manners; here he creates surprising order and serenity. The steel plates have the rich tone and silky texture of Hermes leather, and are attached to both sides of the structural frame with 15mm spaces between them to create a geometry very similar to that of a tatami matted floor. The walls appear to levitate 150mm off the ground plane, strengthening the illusion that they have flown in from another planet, like the astronaut's capsule in the period room at the end of 2001 -- A Space Odyssey.

A tall narrow foyer links the concourse to a second entrance off the hotel driveway, and leads into the gallery. A maple-strip floor and folded maple soffit flow beneath and above steel-clad blocks that divide the long rectangular space into four symmetrical rooms, or pivot to define two linear galleries. The separation of the planes, like the spacing of the plates, gives depth and dignity to the room -- exactly what is missing from the stage set beyond these walls. The slot at their base reveals passing feet on the patterned marble, but you feel protected and contemplative within. The plates invite your touch, and they serve as a scaling device for the paintings, which are suspended from the steel by magnets. The magic soon ends: visitors exit through the inevitable gift shop and are quickly swallowed up in the throng.

The Hermitage satellite opened last October with an exhibition of classic modern canvases appropriated from preRevolutionary collections, supplemented by later work from the Guggenheim in New York and in Venice. Koolhaas also designed the Guggenheim's own 6400 sq m exhibition space within a void just off the casino. Here the collision of styles is even more violent, as marble and faux brocade abruptly give way to a wall of ribbed polycarbonate, raw concrete floors and a tilted aluminium canopy spelling out the name in massive block letters. The hangarlike space rises 23m to a grid of steel trusses and a skylight that can be blacked out by a telescopic blind, painted (in a wonderfully tongue-in-cheek spirit) with a reproduction of the Sistine Chapel ceiling. High winds blew it off a few months after the opening, so visitors will be denied this added treat until it is restored. However, they can take a free peek into the soaring volume through the glass wall of the walkway as they enter the hotel from the park ing decks.

The north wall doubles as a media screen, and part of the south wall, boldly painted in red and black chevrons, pivots open to allow the largest works of art to be trucked in. These can be lowered into place by an industrial bridge crane that is suspended from overhead tracks. An open trench reveals the lower level galleries, which are reached by a 10m wide staircase and escalator. The trench can be covered, wholly or partially, with massive plates to provide a single enormous gallery.

The Las Vegas Guggenheim was launched with The Art of the Motorcycle', a dazzling historical survey that Edwin Chan of Gehry Partners previously installed in the Wright rotunda in New York and later at Bilbao. Chan's vortexes of polished stainless steel (a nod to Serra), steel mesh drapes, and a polished steel ribbon that arced over the stair and into the basement gallery, matched the scale of the space, and mediated between the bare shell and the sensuous lines of the bikes, which were displayed as sculptures. It is hard to imagine this huge volume being better used.

In these two galleries -- one intimate and tailored, the other raw and expansive -- Koolhaas has displayed the range of his skill and the potential of his primary material, slicing through the stucco fakery as though it were a wedding cake, and exposing the steel to lure tourists to unanticipated delights.