By simulating a section of the Scandinavian Ice Sheet over a deep fjord, we aim to understand the behaviour of ice sheets over rough landscapes. For perpendicular flow, we find reduced speed within the fjord and reverse flow at its base. Comparing real and smoothed topography shows that low-resolution models fail to capture these effects. Our findings have implications for Greenland ice sheet models, as commonly used bedrock resolutions likely overlook the influence of similar rough landscapes.