Astalon: Tears of the Earth

Don't stress about this one. Towards the end of the game - somewhere around Ruins of Ash (perhaps after you've beaten the third gorgon) - Epimetheus will let you 'Reveal Map' for 15,000 orbs. That shows you every square you're missing, except a couple in a secret dev area in the bottom-right (where you'll see an Epimetheus statue marker).

There's also an item on the Eastern side of Gorgon Tomb (approach with Algus from Mechanism) called 'Ring of the Ancients', which marks every room on the map with an item left to find.

Put those together and you'll know exactly what you need to finish this off.

If you'd like to have a map to help: https://steamcommunity.com/sharedfiles/filedetails/?id=25080...

The map is from Demajen, who does amazing guides for Metroidvanias. If you'd like to thank him -- buy him a coffee at https://ko-fi.com/demajen

EDIT: my final room was above the save point at the start of Mechanism. You need to throw one of Zeke's magic blocks so it's hanging over the left-hand edge of the column Kyuli is sitting on; then leap off the block to reach the left-hand wall, and climb it. The same room also has a health upgrade. It's hard to spot because it's an "interior" room with four others surrounding it, so you can't see the grey outline.