Another quite famous one, yet you hardly ever see pictures of it, even though it was copied (after a fashion) in the Biltmore estate of South Carolina. When I visited the castle on a tour of the Loire, I happened to know it was Leonardo's design - we found no reference to it on the location.
The most interesting thing about these stairs, to me, is that they were fitted to the castle later on. Leonardo must have been beating his brains out on how to get nice relatively regular divided floors, as those, already in existence, were of different heights.
He solved the problem by cheating in various ways. To start, the stairs are not parallel with the balustrades. Then, stairs arrive at levels different from the floor heights, so you have to go up and down extra steps to enter the building.
As it turns out, the Vanderbilt copy is not a real copy at all - apart from the fact that it turns the other way, the architect had a much easier job.
And so, naturally, it is of proportionally less interest.