The steps leading up to the street from Salts Mill, worn by hundreds of feet every day, thousands if not millions over the years. And I very much doubt whether they are the original ones.
You know sometimes when you're working a lock, you can't help but be standing in a puddle? As Pete pointed out to me at the AGM, that's not coincidence; that's a hollow in the stome worn by the boots of those who worked the lock before you. And I find that a pretty amazing thought.