Deep Stone Wall

Deep Stone Wall is a placeable object used for building and decoration. It functions as a wall-type structure and can be placed like other construction objects to shape rooms, passages, and enclosed spaces.

It can be destroyed only by a Demonic Pickaxe or any better pickaxe. That makes it a relatively durable building piece, so removing or replacing it requires late-game mining power. When planning a build, make sure you are satisfied with its placement before setting large sections of it down, since dismantling it is not a quick early-game task.