I am ridiculously impressed by the method of loci and PAO systems.
To the point that they had me baffling at my own brain. I recently finished Joshua Foer’s Moonwalking With Einstein, and was inspired to give card-memorizing a go. So I built a PAO system while at work, made a quick mental map of my grandmother’s home, and pulled out a deck of cards. I must have spent something like 8 minutes going through the deck in chunks and placing triggers, and then, with rather low expectations, handed the deck to my mother.
And I was able to recite the entire thing back to her.
I wasn’t very quick about it, but I did it. All 52 cards on my first go.