The Matter of Time in Guggenheim Museum Bilbao.
1994–2005, is an installation comprising eight pieces of torqued ellipses made of weathering steel (COR-TEN steel). It is incorporates a series of seven sculptures:
 made of spot-welded sheets of steel that form 14-foot (4.3 m)-high curling walls.
 positioned around the existing sculpture, Snake (Serpiente), that had been commissioned for the museum’s opening in 1997.
This huge permanent installation of eight bent steel sculpture is possibly the largest installation to ever be housed in a museum gallery. The work weighs about 1,200 tons, is over 430 feet in length and has taken up residence in a 32,000 square foot gallery. The eight pieces swirl and glide together, creating spaces while imposing upon the space they are in. Imposing as they may be, the sculptures invite the viewer to become participant: to explore around them, to find the spaces within, to play with sound, to stop and start at any point, to move at any speed. Because of its mazelike structure, this installation will leave different imprints on every person that passes through the experience.