What is the secret to the moon door next to the weeping waterfall in Fez?

Question

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?

Answer 1

The door can be opened using its inscription as a cipher.

Solution:

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.

Answer 2

A translation guide from the fez wiki states the following:

Read in normal vertical orientation, however, the symbols translate thusly:

Use the above cypher when reading rune sequences from TOP to BOTTOM. You must stand under the tablet with runes, or under a set of runes on a wall, and tap the button combinations on the controller with less than a second of time in between for the code to work. You will get the Cryptographer Achievement the first time you input a code correctly.