Pillars
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
In A New Reign for Don't Starve Together, 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.
Gallery
Ancient pillars change color during the Nightmare phase of the Nightmare Cycle.