Yes I know of the 4th location. However I’m checking all 4 spots and I’m not seeing a box, which leads me to believe there is a 5th spot. I’ve checked the area by idol, the left side of the second courtyard, the upper right guard tower of second courtyard, and the area to the left of the dungeon entrance. Nothing.
Outside of castle.
Inside of castle.
There are only 3 spots outside, nothing inside.
Well I did finally find the 5th spot. Using your link, I found it in the lower left tower of the first courtyard. Wish I could super impose the map over this and draw all 5 spots.
https://www.grimtools.com/map/markers/shrines/632
Only ever found the TT in one of the 3 spots. Just saying …