Integrating seismic reflection profiles, well logs, and field evidence with GPS velocities from a network installed in Calabria, southern Italy, we have discovered that the Crotone basin is gliding toward the Ionian Sea over a buried viscous salt layer. This previously unknown megaslide (~1000 km2) is characterized by an onshore updip extensional domain and an offshore downdip toe-thrust rim. The GPS velocity from the Crotone station is significantly higher than velocities from other stations in the region and differently oriented. We ascribe at least part of the anomalous GPS velocity from the Crotone station to the seaward motion of the megaslide or part of it. From the GPS velocity and other evidence, we obtain a viscosity of the buried salt layer within the known range of rock salt viscosity in nature.