You might remember a long while back, Cinema 4D Artist and modeler, Shane Benson, covered (pretty extensively), Subdivision, or Sub-D Modeling in Cinema 4D. The tutorial series covered everything troublesome about Sub-D modeling, from creating great topology, to handling beveled edges, and transitioning shapes. One of the things that people seem to get hung up on when sub-d modeling, is creating odd shaped holes in surfaces.
Shane spent a couple of tutorials looking at how to create odd shaped holes when modeling in general, and has chosen to add another to the series. Here, Shane Benson posts Sub-D Modeling in C4D – Lesson 19 – More odd shaped holes for practice, showing how to approach modeling a semi-sphere depression, in another depression, along the surface of a model.