Endoscopes provide real-time, high resolution video views of the interior of hollow organs and cavities that exist within the human body. Although endoscopic examinations are mostly non-invasive, the procedures still require some sedation or anesthesia to reduce patient discomfort. X-Ray Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are non-invasive diagnostic imaging techniques that display internal anatomy in cross sections called slices. For the most part, radiologists view the 2D cross sections and create mental images of the 3D structures present in the study. However, many of the tubular structuresthat exist in the body have complex morphology, passing back and forth through the cross sections. This paper illustrates techniques for the internal exploration of CT / MRI data that have been reconstructed into 3D surfaces. The views produced by the new methods simulate the types of views that can be obtained with endoscopes. Examples from the brain, cranium, chest, and abdomen illustrate the techniques.