there's a bit of pine outside of the kamisato estate too!

There is actually pine wood in mondstadt like some other commenters say, just hit the tiny trees and you might get pine wood!! :D

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Wuwang Hill has a whole forest of Pine wood but my No.1 location is still Monstadt. The trees are so close to each other and it's so easy to get them with Claymore charged attack.

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You actually can get them right inside the Mondstadt itself. You don't have to endure the sheer cold of Dragonspine.

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There's some in Qingyun Peak , right next to the statue of the seven( north west of the statue)

Wuwang Hill has a lot of them, especially around the domain.

Also in Wuwang Hill