It's a large house, with subtle defenses. There are ornate but functional bars across the windows, and is built of stone.
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15 or better
The decorative crenelations on the roof are actually functional: there are probably archers on the roof. In addition to the guard hidden behind the gate, there are murder holes above the doorway. Arrow slits are cleverly disguised in the facade.
20 or better
A rectangular depression in the dirt projecting from one side of the house indicates a hole was once dug there.