Topological properties are global features that can be useful for recognition of digital objects. For example, this is the case for objects having complex shape without being decomposable into meaningful simple parts. In the case of 3D binary images, topological features are the object components, cavities, and tunnels. While object components and cavities are easy to define and identify, no computationally convenient way to find tunnels is, to our knowledge, available. The aim of this paper is to fill this gap by presenting a convenient procedure to detect and represent tunnels in 3D objects.