The Serpentine Gallery Pavilion has, over the last 13 years, established itself as a must-see architectural event of the London summer season, not only for its experimental structures - which have allowed A-list architects like Zaha Hadid, Frank Gehry and Jean Nouvel to realize their first built projects in this city - but also for the glitzy parties and intellectually rigorous event marathons that accompany the structures. The latest pavilion, which opens to the public tomorrow, responds to the history of previous pavilions on the site (a lawn adjacent to the gallery, in Kensington Gardens) and imagines an archaeological dig through the remnants of structures past to reach groundwater, celebrating the unseen natural water level below the city. Humble but daring, this romantic approach is the result of a collaboration between the Swiss architects Herzog & de Meuron and the Chinese artist Ai Weiwei, who are known for their design of the Beijing National Stadium for the 2008 Olympic Games. While this is not, in fact, Herzog & de Meuron's first completed work in London - their Tate Modern opened in 2000 - it is Ai's first building project there. The landscape created by the dig - the interior of the pavilion, which contains seating for visitors and events - is lined in cork to create a soft, surreal environment shaped by the "ghosts" of pavilions past. Eleven columns, each of which represents a previous pavilion (there was no pavilion in 2004), and one that represents the new structure, support the roof, a floating platform with a circular pool of water that reflects the sky (and which can be drained for special events). As in past years, the pavilion will be the site of Park Nights, the gallery's public events program, as well as its annual Serpentine Marathon, a series conceived by the gallery's co-director Hans-Ulrich Obrist. A new twist, however, is that the gallery, which has sold past pavilions to recoup the costs of their construction but has never publicly identified the buyers, announced that this year's pavilion has been purchased by the billionaire Indian steel magnate Lakshmi N. Mittal and his wife, Usha. The Serpentine Gallery Pavilion 2012 will be on view through Oct. 14.