This work is concerned with the comparison of measurements and predictions of high-frequency electromagnetic wave propagation in curved confined spaces. For this purpose, measurements have been performed at 120 GHz (D-band) in curved prefabricated stoneware tubes. A ray-tracing tool based on geometrical optics and ray density normalization is used for the simulations. The comparisons reveal that an appropriate ray-tracing approach is able to precisely predict wave propagation in curved geometry. It is shown that the actual shape of the boundaries has a major impact on the propagation characteristics compared to, for example, the materials parameters. Furthermore, the effect of the focusing of energy was observed in both measurements and simulations. In this case, the ray density normalization allows us to overcome one of the major disadvantages of conventional geometrical optics: its failure at caustics.