Within the history of recordable human media:
I would take part in tearing down the berlin wall, and I would soak up the unbelieveble energy all around me. The soundtrack to this would be Albion - Air (palefield mountain remix), or some other inspiring, joyous, energetic track.
Otherwise:
I would witness the creation of the universe. It would be just me, and my soulmate (who I have not yet met), having a romantic, intimate experience just watching the incredible view. Of course, we would need a different perception of time, like one present earth second being equivalent to a half million years. The music playing would be the most beautiful, deep sounds to ever reach an ear. It's like how a certain sight makes you feel a particular way, and a sound can do the same. The sound to be heard during this experience has to be just as awe-inspiring as the view.
I like this thread
peace,
Dave