Edit: OK, so Masochist has been reported as a bug several times already. Sorry. Consider this verification that it's happening to me too, then.
I think there's a bug related to unlocking the Masochist achievement (Spend 100 hours in the dungeons). Steam says I have 252 Hours of playtime, yet I still haven't unlocked it. I'm not leaving the game running on the Kingdom screen overnight, and I'm pretty sure at least half of my playtime has been inside dungeons (unless puzzles / class challenges don't count?).
Or is it supposed to unlock after 100 hours of playtime, be they in dungeons, the kingdom screen, or wherever?
Steam's Global Achievement stats suggest that 0% (less than 0.1%) of players have unlocked it, so I'm guessing its unlock is buggy for most everyone, if not everyone.
Should it have a progress bar, as players' hours get closer to 100?