If this is known/has been stated before, my sincere apologies!
When following the pathway parallel to the rock giant and taking a right, there are two cages in the middle of the room suspended over a pit, the left one can be unlocked and then ridden down like an elevator (it drops you off on the walkway that has the first set of swinging blades).
Once activated, the effect seems permanent, thus creating an easy shortcut to bypass the blades/boulders section of the fortress.
When following the pathway parallel to the rock giant and taking a right, there are two cages in the middle of the room suspended over a pit, the left one can be unlocked and then ridden down like an elevator (it drops you off on the walkway that has the first set of swinging blades).
Once activated, the effect seems permanent, thus creating an easy shortcut to bypass the blades/boulders section of the fortress.