I have shown this position to most of my chess students during the past two weeks. None have solved it, although several have seen checkmate patterns that look promising. The position arose in the thirteenth match game Schiffers -- Chigorin, St. Petersberg 1897.* It also appears in Encyclopedia of Chess Combinations, 5th edition (2014) as number 2386. It was brought to my attention two weeks ago via Renaud and Kahn, The Art of the Checkmate (1953).
Black to move
Mikhail Chigorin played 24...b6 and the game was drawn by repetition ten moves later. Renaud and Kahn point out that Chigorin missed a checkmate in five, and their solution is identical to that given in ECC. However, White has a defensive resource that delays checkmate one move, so it is actually a checkmate in six.
Knowing there is a forced checkmate, I was able to work out the five move solution in a few minutes. The computer showed me the additional defensive resource.
Several of my students found the first move easily, but because they could not find the second move, they revised their first move. Alas, all other first moves by Black allow White to unleash an attack.
I think the final checkmate pattern is hard to imagine from this position and that is why Chigorin and my students missed the combination. The solution was pointed out shortly after the game by R.J. Buckley, according to James Mason, The Art of Chess (1905), 210, where the position was represented by a diagram missing the c2 pawn (see Edward Winter, "Schiffers v Chigorin," Chess Notes 7932 [13 January 2013]).
*This game was Chigorin's foray with Damiano's Defense (see "Opening Disaster: Damiano's Defense").