The Thyphlo Ruins are completely shrouded in darkness, and they can only be accessed/exited from the west or by teleporting away. They're surrounded by a bog, so they can't be accessed to by swimming. The ruins can be paraglided into, but the sudden cover of darkness may completely disorient the player upon landing. The veil of darkness begins in the middle of the bog, well before the visual limit of the dome. The ruins feature several bird-shaped spires whose beaks point Link towards the general path leading to the Ketoh Wawai Shrine. It's encouraged that Link lights them for orientation. There are also Fire Rods and other fire weapons available to use. There are no overworld quests or NPCs that lead to the ruins.
Though they are luminous, Ancient and Elemental weapons other than the rods are not bright enough to be useful inside the ruins.
These ruins are filled to the brim with Zonai statues similar to the ones in the Zonai Ruins. However, statues and figures seem to be placed grouped right next to each other, implying that they were placed haphazardly, or further implying that the ruins were a depository for the Zonai statues.
It's not known why the ruins are shrouded in darkness, but clearance of the Shrine Quest does not remove the permanent darkness status. The ruins can be navigated via the use of torches or other luminous resources like Daruk's Protection; if the proper DLC has been downloaded and installed, and provided that the player has cleared EX The Champions' Ballad, the Master Cycle Zero can be used to navigate the ruins by using its front light.
Nearby Shrine Quests
Nearby Korok Seeds
Shoot the balloons that appear near the pinwheel.
Mod of the game showing the Thyphlo Ruins without darkness - by Trollsquad57
Thyphlo Ruins With Master Cycle Zero - by https://www.youtube.com/channel/UCOFduo7n3yGQPmA5egVN-kA