How to Make a Bottomless Pit

A bottomless pit is impossible, right? Wrong! Here's my theory:

First, go out into space to somewhere that gravitational effects of other celestial bodies are negligible. There, build a giant hollow torus at least thick enough to allow a person to fall within it freely. Put something of considerable mass in the donut-hole to serve as a gravitational focal point (you can alternatively build the torus around a large celestial object in the first place). Cut a door into the outside of the torus and lure your victims in--then seal it, just in case. Ta-da! Bottomless pit!

Edit:
I've modified someone else's picture to help illustrate the concept. Just imagine something massive in the middle, okay? Oh, and the door probably isn't to scale--scratch that, nothing's to scale.