It's the Great Peacock Moth Caterpillar.
See Wikipedia for other images, including a painting of the moth by Van Gogh.
Saturnia pyri, the giant peacock moth, also called the great peacock
moth, giant emperor moth, or Viennese emperor, is a Saturniid moth
which is native to Europe. It is the largest European moth, with a
wingspan reaching 15-20 cm.