The Deeper is an area of the map you'll visit during the DLC story and can return to any time after. This area has multiple bottomless pits to kick zombies into. If you are doing 'The Deeper' main mission, you can use Veronique's Head as bait to lure the zombies near the bottomless pits to easily kick them. Otherwise, you'll want to use bait or position yourself in a way to get the zombies close enough for easy kicks.