×I've done some googling, and managed to find one useful site which gives Dudeneys 17 move solution, but this leaves me about 7 turns too short. The 16 move solution on the same website doesn't end at the top right, and has some other problems with it too, and the restrictions Dudeney put on it really make it look as though that was the intended one.

But it just doesn't work!

I count 32x4 moves for dropping the trapdoors, plus 3 to start and 31 to finish. That leaves me with 74 moves.
Now, with Dudeneys solution you travel over each of the crumbly walls once, which takes away another 49 moves, leaving 25 for sword turning, ie 12 changes of direction allowed, thats far too few. So somewhere in the solution I have to spoil the niceness and fill in some of the 2x2 blocks the first time through, not leaving the other diagonal, if you know what I mean..

But I'm still of the opinion Dudeney's one was intended..
So, what am I doing wrong?

×You don't pass through every single crumbling wall. Some squares you pass through twice, but to minimise the total number of moves, consider ways to pass through the maximum number of squares just once. It'll save you a couple of moves each time.

I'm aware of two 17 (bishop) move solutions that will allow you to reach the tar in time. One is perfectly timed, the other is two moves better. Anything more than a 17 move solution would require too many sword turns.

×Complete the first square, then move another 3 up NE, complete the last square, then move another 3 NW to the edge, completing the last square, and continue from there

×A google search for just 'Bishop's tour' should find you a link that will help