The Hidden Doors of Professor Layton
The strategies we employ, such as haranguing offspring with our years of accumulated wisdom (such as how to clean black, rotary dial telephones using Q-tips dipped in isopropyl alcohol) normally leave our families mounting interventions against causing 17-year-olds to weep and gnash their teeth in the captivity of boredom. I think thrusting Professor Layton and the Unwound Future into our hands and solitary hours of retirement is a brilliant move, as may be suggested by the puzzle illustrated.
That's a sliding block puzzle, and the idea is to slowly move the gem around until you eventually slide it out the north edge. This particular one, found behind the Hidden Door of the third game in the series, may be the hardest yet revealed, and a really nasty personal rejoinder to those of us who've been moaning about how easy these puzzles have gotten of late.
Almost... There is a worse... Kids who encounter it too early return their games to the Used Videogames shelves, where we oldtimers pick them gleefully up for a song.
The top secret Hidden Door is a feature of all three games in the Professor Layton series. Getting them open is a puzzle in itself, because the passwords and keys are buried in the next game of the series. Or possibly in the prequels as well as the sequels, I'm not sure.
At any rate, as long as you've got all three of the games released so far in the U.S. (and these are not the same in details as the U.K. versions!), you can unlock the Hidden Doors in all three games, whether or not you've played the the main storylines to conclusions. Fascinating.
For example, the "Hidden Door of St. Mystere" password on my DS Lite is
4B7F8F1B. That gibberish is keyed to my unique DS console (possibly as a function of its serial number), and unlocks the Hidden Door in Professor Layton and the Curious Village, but you find it in Professor Layton and the Diabolical Box, the sequel to the first game. The number will unlock "passwords" that go with other games in the series, a rigamarole best described here.
If you can get through that you're safe from the ravages of dementia, at least for the time being. (ADHD is your problem, dudes. Where's my Pratchett book?)