In microfluidics confocal microscopy and PIV are well-suited instruments to analyze laminar and complex fluid dynamics. However, these analysis methods require transparent devices made of e.g. glass or silicon rubber. This prerequisite of transparency precludes investigations of complex geometries generated by modern 3D printing techniques. Yet, 3D printing enables the engineer to free-form fabricate chemical engineering devices of any complex fluidic architecture. Based on a 3D printed meandering channel reactor with incorporated staggered herringbone structure we exploit the limits of 3D flow magnetic resonance imaging (MRI) for the analysis of fluid dynamics on a sub-millimeter scale. We visualize the 3D flow field, in particular the secondary eddy flows and derive shear rate maps. CFD simulations of the virtual shadow are in agreement with our experimental findings and proof that flow MRI gives reliable experimental access to non-transparent flow geometries.