This invention provides a system and method that allows a therapeutic device, such as an atrial fibrillation microwave ablation catheter or ablation tip to be guided to a remote location within a body cavity and then accurately immobilized on the tissue, including that of a moving organ, such as the heart. In various embodiments, the system and method also enables accurate movement and steering along the tissue, while in engagement therewith. Such movement and engagement entails the use of vacuum or microneedle structures on at least two interconnected and articulated immobilizers that selectively engage to and release from the tissue to allow a crawling or traversing walking across the organ as the therapeutic catheter / tool tip applies treatment (AGE devices). In further embodiments that lack a movement capability (AID devices), the immobilizers allow a predetermined position for the introduced device to be maintained against the tissue while a treatment is applied to the location adjacent thereto. In the exemplary AID devices, variety of steering mechanisms and mechanisms for exposing and anchoring a catheter against the underlying tissue can be employed. In the exemplary AGE devices, a variety of articulation and steering mechanisms, including those based upon pneumatic / hydraulic bellows, lead screws and electromagnetic actuators can be employed.