An enchanted hill in Britain, probably in Wales. The Growing Lookout had a mysterious property of growing by about fifty times its normal size without warning, and from the top of it, a person could see the entire island of Britain.
Lancelot rode by it on the way to Arthur’s court to fight Valerin, but could not stop and examine it because of his haste.
Source
Lanzelet | Ulrich von Zatzikhoven, c. 1200