Digger Tunnel

The Digger Tunnels are large tunnels dug by the Hag 1 while heading to the Cauldron Keep in Banjo-Tooie.

Banjo-Tooie
In Banjo-Tooie, Klungo is fought Inside the Digger Tunnel that connects Spiral Mountain and Jinjo Village. Once beaten, the tunnel cannot be re-entered.

Klungo is later found again Inside Another Digger Tunnel that connects the Pine Grove and the Wasteland, although the Talon Torpedo move is required to access it. Once beaten, it also cannot be re-entered.

Banjo-Kazooie: Nuts & Bolts
In Banjo-Kazooie: Nuts & Bolts, the first Digger Tunnel can be seen in Spiral Mountain, although it is blocked by rocks. An Information Speaker also provides information about it, stating it once led to the Isle O' Hags.