In outside is a cylindrical steel tower, a cauldron form in upper, transparent roof, iron drawbridge, 3 doors, one window where the B.O.B. and moat with purple toxic slime. Inside is full with pipes, lights, electrical lamps in roof and a elevator. In different floors contains gatehouse in lower, gun chamber in middle and garage in upper.
This keep was built when Mingella and Blobbelda decided to go on with their lives together leaving home in Bad Magic Bayou. On mountain where it was built the castle was covered with ice because of the Freezing Furnace until Grunty Industries pollution warmish all ice. When the B.O.B. was created, the upper tower moves aiming at the chosen target at the time the weapon is activated.
2 years ago when Gruntilda's Lair was destroyed, this keep was became the refuge of the same for the plan to suck life forces across the whole island. This fortress began to be invaded by the duo after the incident with Bottles and King Jingaling. Here was the battle with Klungo for last time, at risk in show business called Tower of Tragedy for save Jingaling & Bottles and fight to the death against Gruntilda Hag 1 where she is finally defeated for good.
Shown on Banjo Pilot when the Grunty Industries is deactivated, the mountain was covered by ice again with the fortress leaving just the upper
- It was never actually necessary to deactivate the laser mesh, as you can just jump through the gaps instead.
- In the Cauldron Keep, there are no stairs going up, but Banjo and Kazooie must climb down stairs to enter the B.O.B. chamber.
- Kazooie again breaks the Fourth Wall upon entering the Gatehouse. When Banjo notes that there's no one there, Kazooie replies that the music has changed (to the boss music) and that they always end up in a fight when that happens. She proves right, as Klungo literally drops in seconds later.
- On the right side of the entrance to the world, a sign that says "Cauldron Keep Secret Exit" is seen. This means that the area Banjo and Kazooie enter the world from is not the actual entrance. However, it is unknown where the real entrance would be.
- This level was an equivalent to King K. Rool's secret sanctum called "Hideout Helm" in Donkey Kong 64.
- This level was originally going to be a fuller world like the other 8 levels in the game, however, was simplified to Cauldron Keep due to time constraints.
- The level called "Castle World" (which is the Miiverse alias of the World Castle in Super Mario 3D World) was planned to be the final level in Banjo-Tooie, but was ultimately cut during development due to time constraints.
- It is also the name of the fictional medieval-themed amusement park called "Castle World", rival of another Middles Ages-styled theme park in the 2001 comedy movie Black Knight.