The Ancient Well is a dark pit located in ThornTail Hollow in Star Fox Adventures. It is inhabited by a lone ThornTail (otherwise known as "Crazy ThornTail"). He claims to have lived in the Well for 50 years. He does not allow Fox to explore the deepest parts without a Lantern.
Near the entrance of the well, Fox will find a Spirit Cave with a Staff Upgrade. After purchasing the FireFly Lantern from the ThornTail Store, he can explore the deeper half of the Well to collect White GrubTub Fungus for the ill-stricken Queen EarthWalker.