Visitors to the Museum of Modern Art in New York had the chance to see an unusual performance on Saturday: Oscar-winning actress Tilda Swinton sleeping in a glass box.

For a performance piece call "The Maybe", Swinton wore a light blue shirt, dark blue pants and shoes while lying on white bedding with eyeglasses beside her.

"Living artist, glass, steel, mattress, pillow, linen, water, and spectacles," a description card said.

Swinton first performed the piece at the Serpentine Gallery in London in 1995. In 1996, she performed it in the Museo Barracco in Rome. There is no published schedule for the piece, which will occur about a half dozen more times through the end of the year, museum spokeswoman Margaret Doyle said.

"The nature of the concept is that it not be announced in advance, nor publicized by the museum," Doyle said.

Swinton, 52, won an Oscar for best supporting actress in the 2007 film "Michael Clayton". Other credits include the title role in "Julia", "Burn After Reading" and "The Curious Case of Benjamin Button."

She is also notably known as the White Witch in The Chronicles of Narnia.