So you've gotten a bit further into Aloy's story but are having trouble getting through yet another puzzle section on the map. Either you need the EXP and skill points, or completionism has taken you. Either way, here is our guide for Horizon Forbidden West Restless Weald Relic Ruin to assist you in finding the code and the doorway to complete the Relic Ruin.

Horizon Forbidden West Restless Weald Relic Ruin Guide – Where Is It Located?
So this Relic Ruin can be found further west beyond No Man's Land. Specifically, it can be found northwest of the Gravesinger village of Plainsong. Much like the No Man's Land Relic Ruin, however, you cannot fully complete the puzzle found here until Aloy has the Igniter tool. Finish the story chapter Death's Door, then head on over once you are ready.
Horizon Forbidden West Restless Weald Ruin Guide – Solving The Puzzle
The Restless Weald Relic Ruin is a bit unique in that it involves a bit more detective work than you would expect. By that same token, it also makes the ruin relatively easy to complete once you know the solution.
As you enter the ruin, check around for a scannable datapad. Now, if you're used to these datapads containing keycodes, you're in for a surprise here. The datapad simply states that the code is “the year the facility was built.” There is just one other datapad in this ruin and it's right next to the keypad door, and it basically repeats this same information.
But first, you'll need the depot key. Circle the outside of the ruins until you come across a set of train tracks. Follow these tracks until you find an abandoned train car. It should stick out since it has distinct blue hatch marks for your pullcaster. But don't move the car closer to the ruins. Instead, move the cart as far away from the ruins as the tracks will allow.

Once you have done this, you'll find a lever nearby to switch the tracks. Hit this lever then push the train car forward until it is parallel with one of the buildings. Climb the car up and you should find an alcove along with a tightrope for you to move across. On the other end, there should be the office depot key.
When you get the key, don't go looking for the code just yet. First, move the train car back, switch the tracks, then move all the way to another part of the depot. This will save you a headache later.
So the keypad code for this ruin is more or less hiding in plain sight. If you keep circling the ruins, eventually you will come across four large numbers meant to be part of a sign from centuries ago. This is not to be confused with the rusted and illegible hotel signs peppered throughout.

Once you have this keycode memorized, head back to the ruins where you found the datapad. Look around and you should find the locked door and data terminal hidden in an upper area. If you need help, try scanning with your Focus. You should find some climbable terrain on the righthand side (that's on the interior of the ruins) which should get you up to the door. Put in the key, input the passcode, and the door should open.
But you're not completely done here. Take a running sprint then jump through the door's threshold. This should have Aloy ride a zipline into an abandoned train car depot. From here, look for some firegleam on one of the walls. Ignite it, then get out of the way. This should open a hole outside where that train car you moved earlier should be waiting for you. Pull the train car into the depot then climb it. The relic you've been looking for should be a few easy hops and jumps away.