We report on a combined spectroscopic/structural study of MOVPE-grown GaAs-AlGaAs core-multishell nanowires, containing thin GaAs quantum well tubes (QWTs) wrapped around the central GaAs core. Low temperature (7K) cathodoluminescence (CL) spectroscopic imaging combined with Z-contrast scanning transmission electron microscopy (STEM) tomography performed on single core-multishell nanowires allowed robust correlation between QWT emission and the nanowire inner structure down to the nano-scale. Besides the core luminescence and minor defects-related contributions, each nanowire showed one or more QWT peaks in the 1.53-1.65 eV spectral region, which correlated with sections of the nanowire trunk having different diameters. Average values of QWT thickness (in the 3-7 nm range) were thus extracted from measured nanowire diameter through the application of a multishell growth …