High-resolution atmospheric modeling in complex mountainous terrain remains challenging because multiscaleeterogeneity, thermally driven circulation, and multiscale interactions between local and synoptic forcing. In this study, we present an extensive validation of the high-resolution ICOsahedral Nonhydrostatic (ICON) model in glacierized alpine terrain using extensive observational data from two HinterEisFerner EXperiment (HEFEX) field campaigns conducted on the Hintereisferner glacier in Austria. By integrating a dense network of automatic weather stations, instrumented towers, Doppler wind lidars, and uncrewed aerial vehicle (UAV)-based vertical soundings, we evaluate the performance of ICON large-eddy simulations (LES) at a horizontal resolution of 51 m across a range of synoptic conditions and flow regimes. The model demonstrates good performance in reproducing near-surface temperature, humidity, and wind fields, as well as the vertical structure and temporal evolution of valley-scale atmospheric flows. The remaining biases in near-surface variables can largely be attributed to shallow stable boundary layer processes that remain unresolved even at this resolution. UAV and Doppler lidar observations further show that ICON captures the vertical thermodynamic structure and dominant diurnal evolution of glacier and valley wind systems well. Remaining discrepancies primarily occur during transition periods, particularly when multiple forcing mechanisms interact, where the model shows reduced skill in accurately representing the dominant flow direction and depth. Overall, these results demonstrate that ICON-LES is capable of realistically capturing three-dimensional atmospheric dynamics in complex mountainous terrain, providing a robust foundation for future investigations of atmosphere–cryosphere coupling and glacier–climate feedback in complex mountain environments.