I prefer the card game classics like blackajck or poker. If i want a real challenge then i try to beat a solitaire by myself with a timer on. I reccomend danish people to read some of the articles by Steffen Johannes Larsen if you like the game of twenty one :)

Card games are very good games for the human brain. Games like blackjack, solitaire and even games like Go fish have a positive effect on memory and your ability to focus for longer.

Personally im trying to learn to count cards in blackjack because you need to have a sharp brain to be able to do this for a longer period of time. I read this interesting article in danish a month ago that got me super interested in card games / Mads Saks.