I find them in the kitchen draw we always keep a couple of funnels close and handy

On a serious note funnels can be a lot of things from rivers,roads,fields or cliffs.

Where ever there is something that will narrow down an area that the deer travel.
Having a Topo map combined with an areal photoof your hunting area will show you the natural funnels as well as some man made funnels such as roads.