Dungeons (as yet) Unrealized

These are just a couple of ideas I have had bouncing around in my head but have not yet been able to flesh out.  I don't want to forget about them - but I'm not yet really sure how to execute on them, either.  If anyone who sees this has fooled around with any of these ideas (or has other ideas or feedback), please feel free to leave me a comment or reach out to me over email and let me know what your experience has been like!

Rapture - the underwater dungeon

I gather underwater is the red-headed stepchild of dungeon settings, and I can see why.  There's a huge amount of complication in the mechanics of moving in three dimensions that cannot be easily reproduced with minis (at least until we have anti-gravity).  You might be able to do something with computers, but that sounds like a massive hassle to me, honestly.  Still, I'm kind of attracted to the idea, maybe out of sheer perversity, but I do think it might require some adjustments and mechanics changes to work well and be interesting.

Instead of operating in three dimensions, the dungeon could be mainly vertical with variations in length and very little depth.  So X and Y axis, but almost no Z axis, to keep things fairly simple.  Most dungeons use the X and Z axis, but rarely use Y.  This would give you the ability to still essentially "look down" on the table, it's just that it's using a different pair of axis.

The main idea I think could be interesting/fun for both players and DMs is nitrogen narcosis / Rapture of the Deep type stuff.  This could trigger on a failed saving throw or CON check and do anything from cause confusion to result in a meeting with someone the PC knows to be deceased.  Probably a random table of results is most appropriate (it would need to be progressive based on depth though).  There’s a great chart on the Wikipedia entry which can probably be used to help figure out how goofed up the PCs might be and what the overall impact is.  Of course, this being the world of the imagination, I could certainly take this idea and apply it to a completely different setting if I wanted - at it's heart it's simply, "there's some weird chemical in the dungeon and as you are exposed to more of it, you can no longer completely count on your own perception."

Less fun, but maybe adding to a sense of urgency, I'd like to incorporate mechanisms for compression sickness.  I don't have this fully fleshed out yet.  It could be a set amount of damage per increment the players rise, it could use the existing exhaustion mechanisms in 5e coated with the veneer of the bends.  Another question is how to make this relevant.  In most situations, the PCs will rise through the ocean patiently.  The key here is probably limited air supply, which would require good timekeeping and a few things that might delay the adventurers.  A multi-part resetting puzzle that takes X amount of time to figure out and X amount of time to manipulate once you know HOW to manipulate it could work.  So could delaying encounters, of course.  I've never been great at timekeeping - I manage to do ok, but if I were going to run something like this, I'd probably need to create some sort of aid for myself, something I could tick off and that was visible to the players and myself and simple to use.  Perhaps just something like a series of ten boxes that got ticked off?  It doesn't have to be at exact intervals, but something that gives the players an idea where they stand.  They should know as well how many boxes it takes to surface safely.

The Gates Instantaneous - the time travel dungeon

This is an area of jungle / swamp where there are nine stepped pyramids. These will be in a very, very rough grid – nothing so regular that it is obvious, though. Each pyramid has a single interior room, at the center of which is a stone gate.  When the players arrive, some gates are filled with a shimmering, nacreous energy, and some are not.  That's the way I've conceived it anyway, but it could be any arrangement of nine entryways in a loose grid.

The payoff for the players is in figuring out that the area is one big 3x3 "Lights Out" puzzle. Stepping through a gate transports the players to a different time, when the pattern of active and inactive gates was different. The more active gates there are, the earlier in time they are. Their eventual goal is to reach the end of time, that is, to “douse” all the gates. Getting back to “their time” through the gates is impossible at this point, so it shouldn't be run before the players have some means to do this (a wish, a tear of time from Deep Carbon Observatory, etc).  I'd kind of like for the pattern to be more complex, but the pattern at 4x4 is not always solvable and I'd like to ensure they don't get trapped.

I've been thinking about trying to do geologic time but it's HARD without just killing the PCs outright. I'm picturing something a little like the gate described in the future/perfect mini campaign which can be extraordinarily deadly - putting them into an era where this part of the land was under the ocean, covered with ice, etc, not to mention potentially populated with whoever created the place (probably something or one bespoke).  It also requires some thought of what happens to the site in the future, which is maybe HARDER to pull off.

It's possible this place could be kind of a fulcrum of an entire campaign, wherein the PCs travel to different periods of time in search of xyz, but I've been trying to stay away from the idea that anything has to happen in any particular order in a campaign.

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