Nice work, I enjoyed it.
I only figured out there were multiple inventory items AFTER finishing the game. I hit restart after winning, and got to see the controls info again, and noticed you can press 1 - 5 to see the different items. :) So I played it more like a general Easter egg hunt, just looking everywhere.
I also had trouble at one point when first going to the tomb, that I didn't have a mouse cursor. I think you'll find the Unity code for showing, hiding, constraining the mouse cursor is different in a build than in the editor (and it's quite annoying to get it all set up right!). But it can be done! Double check that the user can successfully alt-tab away from the game and back again, and still have a working cursor, if possible. Then you'll know you've got it right.
Cool atmosphere. :)