Located on the top of Isle O' Hags, was a steel tower contained the lasers grids on doors and toxic moat. It was in this tower that Gruntilda used the B.O.B. for suck the King Jingaling's life force and part up of tower moves when B.O.B. is activated. There were also gatehouse where the double battle with Klungo last time, show business called Tower of Tragedy where Banjo and Kazooie had to risk for win and save Jingaling & Bottles.
In Hag 1 parking inside the rooftop, the double they fight to the death against Gruntilda with her sisters' drill to be defeated again.
- 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.