Hyrule Castle Town Ruins Well
Tears of the Kingdom
As you enter the second chamber, the chest is visible behind bars in a central column with a horseshoe-shaped moat around it. There are two dirt platforms along the moat with Horriblins on them. The chest is accessible from one of these platforms, via a tunnel lit with Brightcaps. If you swim along the right side, stay to the right at the fork and look to your left at the first dirt platform. Swimming along the left side, it will be to your right on the second dirt platform.