Three hidden defensive (where this to be a real castle) passages can be found built into the tower walls of Lever Castle. These would provide access to strategically placed 'arrow slits' or 'bow loops' around the circumference of the towers. The arrow slits are narrow vertical windows through which archers could shoot arrows.

Lever Castle has two hidden passages built into the walls leading off from the Main Staircase. The upper passage inaccessible since the collapse of the staircase is shown in the photograph.

The upper passage is only a small section, but the remains of the passage floor can be seen on the upper part of the wall. This passage would lead to an arrow slit facing away from the reservoir.

A second passage, easily accessible at ground level will be found to lead off from the foot of the staircase that curves round the opposite side of the tower and commands an excellent view along the side of the castle and down to the reservoir.

The lower passage often features in children's games of hide and seek and is often known as the secret passage.