Found this door by accident. There is a moon door that appears on the side wall of the weeping waterfall node.
Does anyone know whether it has any use? Or is it just an Easter egg from Lord of the Rings, as it only shows up at night?
The door can be opened using its inscription as a cipher.
That door is only illuminated at night, but you can enter the code any time of day: ← LT ← → RT ↓ ↑ LT. This code is different from that of the nearby pillar.