Janet Cardiff and George Bures Miller. I adore her/their work and am so glad to have been able to see their work here at the Museum of Contemporary Art.
She does "walks," art pieces in which you put on headphones and, well, walk, while listening. I did Missing Voices: Case Study B in London, a walk that goes through part of the East End, through streets where Jack the Ripper walked/killed. You hear whispers and footsteps...amazing. If you ever have the chance to see their work or go on one of the walks, you MUST do it!
Bonus: the fantastic view from the back of the museum.