Got a few hours to spare? Why not go see the RSC's production of Tantalus at the Barbican, directed by Peter Hall? It's only ten hours long...

This pales alongside Ken Campbell's 24-hour play, Warp. I was almost tempted to go see this last year in some Bankside arches as part of some new-age-clubbing-juggling-fire-eating-tree-hugging hennnaed happening. However, if you have just 18 hours to spare, you can watch Warp in the comfort of your own home on video.