In the back of the boss arena in the temple of day and night, there’s a nearly invisible chest. It’s possible to just barely see a bit of it sticking out from the wall but it seems to otherwise be stuck behind the wall. It can still be interacted with and looted with no issues.
I confirmed it’s not a one-time thing and respawns as I’ve looted it twice now.
When it’s opened it becomes completely invisible but can still be looted.
