The puzzle starts out with the following position:
However, the puzzle line given by the site is a prime example of how a computer line is not always the crucial line that you need to calculate as a human. On the site, after 30.. Bd4+ you need to solve the puzzle after 31. Kh2. The line continues with 31.. Be5+ 32. Ng3 Bxc7, which wins black the queen:
The more complicated line to think about is what happens after white plays 31. Kh1. The computer would never make this move because it leads to mate, but it is a mate that is crucial to see when solving the puzzle. After the obvious 31.. Qxf1+ 32. Kh2, here is the crucial part of the puzzle:
This position is a mate in 3 problem waiting to be solved with 32..Bg1+ 33.Kg3 Qf2+ 34.Kg4 f5#. It's a beautiful mate:
It's an example of how using the computer line does not necessarily test whether someone has really solved the chess puzzle. To the computer it is obvious that 31. Kh1 leads to mate, and therefore it would rather sacrifice the queen with 31. Kh2. However, the former line is harder for a human to calculate and thus more crucial to test.
I hope you enjoyed this puzzle as much as I did, and I encourage you to use lichess to train your chess tactics.