Empty plinth and blank piece of paper to feature in exhibition of invisible art Also in the exhibition will be Warhol's work Invisible Sculpture - dating from 1985 - which consists of an empty plinth, on which he had once briefly stepped, one of many explorations of the nature of celebrity. Another, 1000 Hours of Staring is a blank piece of paper at which artist Tom Friedman has stared repeatedly over the space of five years, and another by the same artist Untitled (A Curse) is an empty space which has been cursed by a witch. Ralph Rugoff, director of the Hayward Gallery, said: "I think visitors will find that there is plenty to see and experience in this exhibition of invisible art. From the amusing to the philosophical, you will be able to explore an invisible labyrinth that only materialises as you move around it, see an artwork that has been created by the artist staring at it for 1000 hours, walk through an installation designed to evoke the afterlife, and be in the presence of Andy Warhol's celebrity aura. This exhibition highlights that art isn't about material objects, it's about setting our imaginations alight, and that's what the artists in this show do in many varied ways. The exhibition forms part of the Southbank Centre's summer-long Festival Of The World with MasterCard. Also featured among the exhibits will be a series of typed instructions by Ono, encouraging viewers to conjure up an artworkin their minds, Jeppe Heine's Invisible Labyrinth in which visitors negotiate their way around a maze wearing digital headphones activated by infra-red beams.