Large, fast-moving glaciers create long, linear mounds of sediments covering large areas. Understanding how these features form has been hampered by a lack of data from the bed of modern-day ice sheets. We give a detailed view of the landscape beneath an Antarctic glacier called Rutford Ice Stream. We towed a radar system back and forth across the glacier to measure the ice thickness every few metres. This is the first place such a highly detailed view of the sub-ice landscape has been created.