In the basement of the Saatchi Gallery is Richard Wilson's <i>20:50</i>, 
a special room.  Looking down, it looks like you're looking deep into a 
pool with a mirrored bottom, but you're not!  It's actually some sort of 
reflective metal liquid that's perfectly smooth, and the colors in the 
rest of the room seem chosen so that when they reflect through the pool, 
it plays another trick on the eyes. <br/>You have to see it to 
understand.