A torque-transmitting, variably-flexible, corrugated insertion device includes a hollow body having a proximal end with an entrance for receiving an instrument and a distal end with a tip for protrusion of the instrument. A vacuum-activated device transitions the hollow body between a relatively flexible condition and a relatively stiff condition. A corrugated tube transmits torque from the proximal end toward the distal end. A method for transmitting torque and variably flexing an insertion device for receiving an instrument includes providing a hollow body, transmitting torque along the hollow body with a corrugated tube, applying suction to create a vacuum in the hollow body for placing the hollow body in a relatively stiff condition, and relieving the vacuum for placing the hollow body in a relatively flexible condition.