This enormous kauri tree towered for a thousand years over prehistoric New Zealand before it fell into a swamp, where the lack of oxygen and fungus preserved it for 45,000 years. Workers snapped two 90-ton-capacity winch cables trying to extract it in October 1994; finally they cut it into two sections of 110 and 30 tons and hauled them out separately.
Then David Stewart built a concrete pad 20 inches thick, placed a 50-ton section of log atop it, and spent 300 hours carving it with a chainsaw and 200 hours finishing it. At 12 feet in diameter and 17 feet tall, the result is the world’s largest (and certainly oldest) single-piece circular stairway … built inside the log.
(From Spike Carlsen, A Splintered History of Wood, 2008.)