A flexible endoscope insertion method includes: rotating a hollow organ by changing the body position to semilateral position or lateral position for observing the lateral wall of the lumen; turning the tip of the flexible endoscope to the lateral wall of the lumen by rotating the flexible endoscope in the counter direction of the lumen; and retracting the organ with the flexible endoscope itself by rotating the flexible endoscope in the counter direction of the lumen. In other embodiments, the method includes: rotating a body cavity by changing the body position to the appropriate position for observing the lateral side of the organ; turning the tip of the flexible endoscope to the lateral side of the organ by rotating the flexible endoscope in the direction of the lateral side of the organ; and retracting the organ with the flexible endoscope itself by rotating the flexible endoscope in the direction of the lateral side of the organ. Methods of visualizing and accessing a lumen interior of the body are provided using the endoscope.