I will give a description of the methodology behind the CO5BOLD 3D model atmosphere code which is in part developed at the Center of Astronomy at Heidelberg University. The code is build to construct high-fidelity models of the surface layers of late-type stars. For this, (magneto-)hydrodynamics and radiative transfer are main ingredients. I will describe projects which illustrate CO5BOLD's capabilities, mainly revolving around high resolution spectroscopy. One cracking story is connected to recent laboratory measurements of stellar opacities with the "Z-machine".