Where do you live? In New York I know folks that do several different things. I let mine go down hibernate naturally outside. (this sort of thing does pose some risks as you most likely (which is the case for me) cannot monitor them once they are down for winter. Mine will be hibernating on hard bottom this year and I put a bubble system in and a de-icer to keep a hole open in the surface of the pond so gases from rotting organic mater do not toxify the fish and turtles.
Some people here will bring in their turtles when temps are nearing constant 40's for about two weeks and with hold food. they will warm soak the animals every day or two for a couple of weeks until their gut is cleaned out. and then hibernate them in tubs of water in their garage. (you must be sure that they are in an area where the water will not freeze solid. Then they just monitor them every few weeks (take them out, make sure they are still moving and not looking poorly and weighing them to see if they are dropping weight too rapidly.) Then the water in the tub is freshened and they sunk down again for another few weeks.
I personally have never done this particular method but the person that I know who has has never lost animal this way yet. (with the natural method -- I cannot in all honesty say that I have been that lucky -- especially last Winter which was so incredibly severe.)
Steve