Typical solitaire is both mindless and you mostly "lose", which is a horrid combination. Spider solitaire is a good mental challenge and you usually can win if you can just figure out how. But I don't play it with real cards because my Perl version makes backtracking easy and I hate not being able to backtrack in solitaire. Freecell is only a moderate challenge but you can almost always win there. But I haven't played any solitaire in months, though I often do puzzles when trying to get to sleep, which is similar.