Inspect each wickerman once it is burning.
You will go past each in the natural story progression in Episode 3.
1) Solitary House - after reading the diary in the basement and leaving the house
2) (MISSABLE) Lighthouse - after fixing the light
3) Donnán Manor - after entering the shed by the mill and getting the iron disc
4) (MISSABLE) Old Abbey - after you opening the secret passage, go back to the entrance, don't go in the passage yet.