I'm sure there are still English speakers on this planet who, when you say "dungeon", immediately think something like the Man in the Iron Mask up in chains, and would never imagine big treasure chests, monsters, or a bunch of people going IN to one on purpose, instead of trying to escape. For a lot of us though, one of the earliest meanings, really crappy prison is all but buried underneath probably one of the most generic and multi-faceted terms in gaming.
 
Of course video games can't really take credit for this corruption of the term. To find the culprit you'd probably have to go back to the 1970's, when Dave Arneson, Gary Gygax and others were creating the first pen and paper role playing games. Perhaps the first dungeon was really a dungeon, but the term quickly became shorthand for any place, usually indoors and filled with monsters and treasure, that player characters would likely delve. The dungeons of Dungeons and Dragons could be just about anything, although there still tended to be a maze-like, oppressive quality to most of them. You'll rarely find someone describing Any Place at All in an RPG as a dungeon, but the old, very specific castle pointers are all but erased, such that a natural cave could easily take the place of a term meant to describe something artificial.
 
Video games, eager to shoulder some of the complexity of their analog bretheren, managed to make the more castle-ish mazes into "dungeons," but the adaptation of dungeon into its RPG equivalent took quite a while. You had MUDs back in the text chat days, Multi-User Dungeons, which preserved the maze-like quality but despite being called dungeons, they could pretty much be anything that text could describe. In a few years, then, video games ran past pen and paper RPGs and made "dungeon" mean pretty much any environment. It wasn't until visual presentations got more sophisticated that video games calmed down and started paying tribute to the pen and paper games that had inspired them.
 
If you're not a gamer of any stripe, you would probably still treat dungeon as a specialty word reserved for ren fair jokes or the playful variety of whips and chains, and you might even mispronounce the word a few times. But I'm willing to bet there are quite a few people who are only cursorily familiar with games who would still know what you were talking about if you used the term more generically, though I imagine many of them might first imagine torches in sconces, chains hanging from the wall, and slimy stonework. Hell, I do too.