Follow the Building Diadwyn quest lead
The current public quest entry for Building Diadwyn sends you to the town of Diadwyn for the block, and the block’s wiki page places the chest at the town’s center. Treat the quest as the lead and the chest as the goal.
This page answers the location task — where the block is. The unlock prerequisites it satisfies stay with the block unlock guide.
Recognize Diadwyn and head for its center
Open full-size image Aim for the middle of town once you arrive; the chest below is the landmark you are looking for. Do not follow the screenshot’s quest arrow — it marked the author’s own objective at the time.
Open the central silver chest
Open full-size image Reading the quest or talking through its dialogue does not add the block to your materials. Opening the chest and taking the block does.
From the chest to the recipe
The unlock rule from the block unlock guide, applied to what you just picked up.
Loot the silver chest
The named block enters your materials.
Obtain one qualifying basic block
Rough Wood, Rough Stone or Plant Fiber Roof — one is enough.
Craft at the Workbench
5 Lump of Clay + 5 Wood Logs → 100 Half-Timbered Blocks.
Spot the chest, then verify the pickup
In the walkthrough’s scenes the silver chest sits near the center of town, by a chair and a tent — use those landmarks once you are in Diadwyn’s middle.
After looting, check the picked-up item reads Half-Timbered Block before you leave. Then the unlock prerequisites from the block unlock guide take over: the named block plus one qualifying basic block.