Obelisks are indestructible Structures usually found surrounding the Pig King in Sandbox Mode. It is used as a decoration around the Pig King, but it also acts as an indicator of the Sanity level of a player. When the Sanity level is 15% and below, the obelisks around the Pig King change their states: the lowered ones raise, and the raised ones become lowered. A strange Shadow Creature resembling Mr. Skitts briefly appears to raise and lower the Obelisks.
In Adventure Mode, Obelisks act as road barriers, and can be great for many defensive ideas. However, it will be hard to deal with, as one might have to eat a load of raw Green Caps to lower their Sanity and Cooked Green Caps to raise their sanity, and it would take a while to defend against something, like Hounds.
Obelisks may be found in one of two states, depending on the Sanity level of the player: raised and lowered. Obelisks in the lowered state will not act as obstacles in the player's path. Obelisks in the raised state will act as obstacles and the player will need to adjust their Sanity level accordingly in order to lower them again. The player cannot use the Nightmare Amulet's insanity effect to raise or lower the Obelisk.
In Adventure Mode the player may encounter Obelisks that will impede their progress if their Sanity level is not in the correct range. In Sandbox Mode they serve as a decoration, which surrounds the Pig King.