The whole deck face down. Turn two, remember everything.
Also called memory or pelmanism. The entire deck goes face down, and the whole game is remembering where things are.
Shuffle a 52-card deck and lay every card face down in a grid — four rows of thirteen, or any arrangement everyone can reach.
On your turn, turn two cards face up so everyone can see them.
If they match in rank, you take both and go again. If they do not match, turn them back face down in exactly the same places, and play passes on.
Suits do not matter, only rank. Some players require the colours to match too, which halves the number of valid pairs and makes for a much longer and harder game.
Play until the table is empty. Whoever collected the most pairs wins.
It works perfectly well as a solitaire: clear the whole grid and count how many turns it took, then try to beat it.
Use half the deck — just two suits, 26 cards — and lay it out in a smaller grid. It stays winnable, which matters more than the challenge.
The one real tactic: when you turn over a card you have not seen before and it does not match, pay attention to where the second card goes rather than the first. Everyone remembers their own first card and forgets the one they were forced to reveal.