At my high school there was a courtyard with a concrete patio where you could look out over a grassy area about ten feet below. One day at lunch I sat on the edge of the patio and tried to imagine what it would be like to fall from that height--how soft would the ground be, how likely would it be that I'd twist something or break something, how far would... and then I just jumped. And I was fine.
I like a straighter "appeal of the void" but I don't think that's as accurate.
As for me, I don't know how to describe it exactly...mostly an intense curiosity or reflection about just how interesting it would be for myself and everybody else if I jumped. After all, you'd be able to see practically unique sights that nobody in the world has seen before...
Wait a minute--all this talk of tingly urges, voids, and aiming makes me wonder whether we're talking about the same thing. When I look over a cliff, I get an if-only-I-could-fly, followed by an irrational maybe-I-can-fly, tempered by a what-would-happen-if-my-camera-fell, which causes my knees to go involuntarily weak.
I discussed this with a French friend of mine a few weeks ago while overlooking Rustaveli Avenue in Tbilisi from a third floor balcony (which are ubiquitous the country over). She had just returned from Stepantsminda, a very beautiful mountain town to the north, to which I have not yet been. Her comment: "It might not be a good idea for you to go; there's a lot of vide there."