Stuck in Castle Braer *Spoilers*

[Tank!]

So I made it through a large chunk of castle Braer, and got a "Key with a Strange Symbol". My guy said he remembers seeing the symbol somewhere but I can't figure out where it goes.

I even backtracked to a ton of old areas and did a optional Entropy rift, got some upgrades, etc. I literally do not know where to go to next, I feel like I've tried all the places I can but still coming up against locked doors I can't open

[Snail]

Old Wickham Monastery - Lower Cemetery. On the left side, before the ascent.

[Ole-Lukoile]

Strangely none of the levers work in there

[Ole-Lukoile]

It is riddle

[Aeshmah]

Read _all_ of the gravestones on each level and the corresponding lever can be pulled.

[StevoRay]

The Strange Symbol key goes to a crypt door on the far left of the map next too a wood material node.

[frostee]

Originally posted by Aeshmah:

Read _all_ of the gravestones on each level and the corresponding lever can be pulled.

JFC they honestly want us to read all kickstarter backers?

[Isaac Schneider]

Stuck at the same place, I have the key as well but no idea where to go