Tobias Island, discovered in 1993 by the German research vessel RV Polarstern, is a system of low-lying banks and shoals hidden in sea ice 70 km off the northeastern coast of Greenland. Here we use satellite radar interferometry and airborne laser scanning to show that this island is 2 km long and 35 m high --- much larger than was originally reported. We have also been able to pinpoint the exact location of a stable area where a new group of small islands may be hidden. This demonstrates that satellite radar interferometry is an effective tool for finding ice-covered islands as well as for mapping them.