The Nessie Carving is treasure that can be obtained in Sly Cooper: Age of Thieves in the episode Braverobber. It is worth 187 coins and the time needed to reach the safehouse is forty-one seconds.
"Legend has it that within Loch Ness rests the mighty Nessie, a.k.a. The Loch Ness Monster. While many hoaxes were created regarding the myth, this carving seems to add credibility to the sightings, mainly because the myth apparently didn't exist until years later..."
It is located on the shores of the loch. Anyone can obtain this treasure.