The nesting meteorite. The box is checked.
I´m starting to think that I may have been careless in my reading of The Bleak Journal. Chapter 12 was the last game that we played on a late night with a couple of beers and long drinks..
Pretty much what happened. When you flooded the cavern to destroy the nest you created a new tiles. Destroy the Underground cavern and replace it with the underground lake. Destroy the other two tiles on the plank.