D&D 5E Need ideas for a city straddling two planes!

[Werebat]

So I am unexpectedly running a new campaign that may begin very shortly. I've been lazily turning an idea over (and over) in my mind concerning a pair of prime material planes that are "close together" enough that travel from one to the other is relatively easy, especially in certain spots. If you remember the twin worlds of Arcane and Myrror from the old Master of Magic game, you're on the right track. Here and there are ancient gates between the worlds that are permanent and were build long ago by another civilization -- or maybe some of them were constructed more recently. Communities tend to crop up around these gates, as they offer unique trade and other opportunities.

One of the worlds is rather wet (lots of swamps), and the other is rather dry (arid lands).

I don't have a lot fleshed out other than that. I'm toying with the idea of adding a homebrewed psionicist built as a set of alternate "bloodlines" for the sorcerer. I have a few races and cultures I'm envisioning.

But I want to start the campaign off in one of the larger cities in the campaign's area, a city that is in some senses TWO cities, linked by a central gate between the two worlds.

I'm looking for ideas on how to flesh out this city and make it more alive. Notable NPCs, curious customs and fixtures, important organizations, unusual inhabitants or trade goods. Simple one liners are great for me to run with.

So have at it! I'm just hoping for a slush pile for me to wade through and pick cool ideas from. Thanks in advance!

 

[Dannyalcatraz]

A powerful rogue NPC- and/or subclass- that can pop back & forth between the two (with limitations, of course) without the use of portals would be cool.

 

[Irda Ranger]

The Keepers of the Green live in the arid world and maintain glass greenhouses (made from local sand and glass made by concentrating the heat of the local sun, but with water imported from the swamp world). They grow plants from both worlds and do a brisk business with herbalists.

The Ankali Lizardmen of the swamp world maintain a undercity that is only accessibly by swimming through long, flooded tunnels. The tunnels are lit, but unless you can hold your breath for 10 minutes you'll drown trying to reach their part of the city. Even water breathing is dangerous, as part of the tunnels pass through the city sewers.

The Society of Seers is always interested in the spice mélange available only in the deep deserts of the arid world.

 

[tardigrade]

It may not be what you want at all, but check out "The City and The City" by China Mieville. It's a police procedural set in two cities that occupy the same physical space but whose inhabitants are not allowed to move between the two (except via an official border at the centre) or acknowledge the inhabitants of the other without attracting the immediate, possibly terminal attention of a (possibly supernatural) secret police-type agency called Breach. It's intentionally left ambiguous whether this is just a bizarre social convention or not but I've always wondered about basing a campaign on it with explicit planar travel.

https://en.m.wikipedia.org/wiki/The_City_&_the_City

(Disclaimer: I've probably made that sound terrible but that's entirely my fault)

 

[John Bravo]

Another book that might help you is A Darker Shade of Magic. It has a series of planes stacked on top of each other with a central point of London.

 

[jasper]

Didn't Piers Anthony do a trilogy on this? One side was science the other magic?
edit to add

Split infinity https://www.amazon.com/gp/product/B00WKNKTC4?ref=series_rw_dp_labf

 

[MechaTarrasque]

The fairly recent release, Sig: Manual of the Planes, had particularly interesting notion that a city connected to several planes could have different planes having dominant connections at specific times. Ebb and flow, and a transition period is a particularly good time to have PC's showing up--the guys about to lose power and trying to limit what the other guys about to get power can do, and the guys about to get power are trying to get as early a start as possible. Most times, it is pretty stable (even in transition), but Big Event X has occurred in the city and everyone is treating a crisis as an opportunity.

 

[Guest 6801328]

Another book that might help you is A Darker Shade of Magic. It has a series of planes stacked on top of each other with a central point of London.

Just reading the title of the thread I instantly thought of Neil Gaiman's Neverwhere.

 

[Ovinomancer]

I always enjoy playing with these scenarios to establish a mythos that turns the usual good versus evil tropes sideways. Given your setup:

These two worlds used to be very different, both verdent and lush, prior to the Disagreement. The elemental lords of Fire and Water became entrenched in a petty disagreement that led to an enmity between the two. Tired of the constant back and forth, the Lords of Air and Earth proposed a plan: these two worlds, close in the Astral, would be brought together to form one. The Lord of Fire would be given dominion of one half, the Lord of Water the other. They agreed, and so these two worlds were forever altered. On one side, deserts dominate, with ancient harbor cities now sitting in ruins next to vast salt pans. Easily available water can only be found near the portals that link to the other world. On the other, mouldering ruins slowly sink beneath the ever rising waters. Only near the portals that allow passage is there dry land.

Now, astride the Great Arch, the City has grown. The size of the portal at the Great Arch and the numerous smaller portals nearby give both worlds the things they lack for a great city to exist.

Traditional farming can really only exist near portals on either side, so civilization clings to where there are portals.

Possible plot: the players find out what the original dispute between Fire and Water was, and can resolve it. Doing so, however, will separate and restore the worlds, causing great damage to existing civilization, but allowing both worlds to flourish once more. The current powers that be on both worlds, though, have that power due to the current makeup, and would not like to see the current state change; however, there are other groups that seek to restore the worlds. The players can try to change everything, or side with the status quo and stop others from trying to restore the worlds.

 

[tardigrade]

One more potential source of inspiration from fiction: Charles Stross's Merchant Princes series, which is about a family that can cross between parallel universes (and uses it for drug dealing etc, until an enterprising businesswoman comes along with better ideas, and then the US government gets involved... it starts to get messy).

I agree Neverwhere is probably the better bet, though.