You will get this as you explore, but if you're impatient and want this as quickly as possible I'll show you the 3 locations I used.
1st one is Ledecestrescire see screenshot where my green arrow is
2nd one is in Norway in Hordafylke, green arrow again. Use atlas on map screen to travel to Norway
3rd one is East Anglia
Don't worry about being underlevelled in Norway and East Anglia, you can use your ship to get close and then do the puzzles without fighting anyone. The puzzles themselves are stacking stones and holding b to confirm.