Thank you to GEB reader Ragnhild for bringing this to our attention. The island of Gorgona off the west coast of Italy appears to be a large lake in Google Earth.
View->Water Surface in Google Earth, for the best effect.
We don’t think it is a case of the altitudes simply being inverted, as areas with a lot of buildings on are probably quite flat in reality, and there are areas where the cultivation follows the (real) contours which lead us to believe the central areas of the island are approximately the right shape, just several hundred metres below where they should be and the steep slopes around the edges are just Google Earth trying to reconcile the conflicting data.
Also try turning on the roads layer and the roads appear to float at sea level.
We have looked at similar effects in the past, including the time Google drowned the city of Crotone, Italy and parts of southern California that are below sea level and show the water surface animation.
Google Earth elevation data can be very inaccurate, especially in mountainous areas, as we have discussed before when looking at Rio de Janeiro.