Ruins Torches, colloquially known as Pyro Torches, are small structures found sticking out of the ground. They are activated with Pyro DMG and remain permanently activated when the puzzle is solved.
Sometimes, they are found in groups of four and are used to unlock the chest on a triskelion platform. These platforms have segments which light up when its respective torch is lit; each segment also points in the general direction of its torch. Once the platform is completely lit up, the chest is unlocked.
Other times only a specific subset of a group of torches need to be activated as part of a puzzle to unlock the chest.
A Loading Screen tip about Ruins Torches reads: "They say the insignia on the platform sealing the chest hints at the direction of the ruins torch. Some adventurers utilize this clue when hunting for treasure."