Greensted Church. Its walls were built out of oaks, cut in half vertically and roughly finished with adzes on the flat side, either some time in the 900's or somewhere in the 1000's - no one is exactly sure. So these shining silver walls are either just barely under, or comfortably over 1000 years old.
You can see from the smaller picture, below, that in other lights, the oak looks black. The brickwork at the bottom is Victorian; the walls were rotting at the bottom and they decided to cut off the lower part and replace it with brickwork, keeping the rest. On the inside they look deep black, and you can see and touch the adze marks.