Story and accessibilityEdit
The Energy Hold is the largest area in Bowser's body and is apparently located in his small intestine, as depicted during the game, Mario & Luigi: Bowser's Inside Story. This area is accessible to Mario and Luigi once they discover Durmite is one of the Star Sages. The plumbers alongside Starlow come here, but they cannot proceed because of three Boo-like Blocks that block the path
Later on in the game, the area becomes more accessible when Bowser uses the Boo-ray Machine in the Tower of Yikk. The Boo blocks then vanish, giving access to other areas. Most of them will require the Spin Jump to be traversed, and the brothers also learn how to burrow underground, as well as collect Attack Pieces from blocks to learn a new attack.
After learning two new moves, Mario and Luigi find Durmite, but she enters a door which can only be opened by a Star Panel. After a few more doors, they battle Durmite, who transforms into Wisdurm afterwards and awards the bros with the first Star Cure. Wisdurm then makes a door accessible for Mario and Luigi. The door allows the two to exit Energy Hold and unlock the Joint Tower.