Tomb in Beggar's Nest

[skywise]

The riddle for the tomb in Beggar's Nest reads:

'A wall at arms length'

So after trying out all the gems I have in the chest I'm thinking 'Agate', unfortunately I don't have one of those
Are there any jeweller's in town? Does anyone know where to find an Agate? Is it even the right answer?

[Yuusuke]

SPOILERS AHEAD

Okay, here goes
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You need to talk to Briley in the Hall of Justice (City Core) to start the quest that will lead you to this door. SOLUTION ahead...
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After you get your three ceremonial items (Sword, Shield, and Arrow) you put one of each in the corresponding chests. A Wall at Arms Length = Shield