Pillars are Structures found in Caves and Ruins. They cannot be interacted with or removed without the use of Console Commands. They can obstruct the player's view and movement, and only serve a decorative role.
Don't Starve Together introduced 2 new varieties of Pillars, Cave Rock and Flintless, matching other resources in the biomes they are found in. While visually distinct, they are functionally identical to the original Cave Pillar.
In A New Reign expansion, a new variant of Pillars can be found in the Atrium Biome. Similar to the Ruins version, they will change colors when the Ancient Gateway is activated.