Decor and furniture
Picture F (Hidden Safe)
When destroyed, will randomly spawn (25%) Wall Safes and (75%) an air block. Do not leave an empty space behind it.
Changes into
When its hit points run out it becomes 
Wall Safe.
Drops when destroyed
Wood× 1-2
Where to find (2 POIs)
Pop-N-Pills Factory (tier 5), NFD Engine 4 (tier 2).
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.