The Rainy City works as a standalone setting, big and varied enough to be the home of multiple campaigns. So far, I’ve used it in three distinct long-form campaigns myself, plus a very large number of one-shots.

But what if you’ve already got a campaign going? How can you use this place? 

Maybe you want to have the PCs visit the place for a while. Maybe even come and go. Can you still do that?  

Absolutely.

Let’s start with the city as a self-contained place, and expand from there to some alternative visions of how to use the city in your own campaign. 

THE SELF-CONTAINED MODE

The City as the End of All Possible Worlds

This is how I play it. 

Some sort of magical catastrophe caused the world to start flooding. Then it spilled over into other worlds, other alternative planes, other dimensions. And the floods just… kept… spreading. 

The city itself was probably the epicenter of the magical catastrophe. Many people in the city think that a wizard did it. The Grand Academy of Magic was here, after all, and now it lies flooded beneath the Murk, that foggy channel that separates the two islands of the main city. Someone in the Grand Academy made a mistake. 

Not just a mistake. A Mistake. 

It must’ve been a Mistake because all the many and diverse worlds of the multiverse are flooding, one by one, and their refugees keep showing up in ships year after year. It takes a long time to flood a multiverse, and many sages believe there are infinite alternative prime material planes, so this could keep happening for a while.

Once people arrive in the city, it’s their new home. There’s no leaving again. Some few people make it into the Nine Swells to Vagabond Bay, but no one ever heads out and makes it back. There’s nothing but storms and sea monsters out there, forever. Most people don’t survive the floods that destroy their worlds to begin with, and of those that do escape by water, even fewer make it to this one last port in the storm. And here they stay.

OTHER VISIONS

The Bermuda Triangle

In this model, you place the Rainy City anywhere in the seas of your own campaign world as a kind of “Bermuda Triangle” within the setting. Maybe it’s distant, obscure, at the edge of the map, and no one knows about it. But there could be rumors. Lost treasure ships. Vanished explorers. A place no one returns from. 

But wait. If no one has ever gotten out, how do we know about it? Give the PCs a map, tell them about the rumors, or just mark it on your campaign map somewhere. Maybe they’ll want to check it out. 

And maybe, in your campaign world, it’s possible to get back out once you’ve gone in…

The Lesser Bermuda Triangle

As above, but people have gotten in and out more than once — it’s just too stormy for regular trade routes, not too stormy for the very best sailors and adventurers to brave the trip at the right time of year. This keeps it isolated, lets it have its own identity, but at the same time lets your PCs visit and return. Very powerful patrons might even pay adventurers to take the risk of entering the storm to find the Rainy City to take a message in, or to beseech one of its powerful wizards for something. Maybe someone on the outside hires your adventurers to go to the Rainy City, steal something unique from a wizard, and come back. 

The Elemental Plane of Water

If you have elemental planes in your setting, you can place the Rainy City in the elemental plane of water. Maybe not all the worlds are flooding, but some do get flooded and the survivors land here.

Or maybe it is the port between your world and the elemental plane of water. If you want to go to the elemental plane of water, first you have to sail successfully to the Rainy City. Then, after resupplying, you can set out from Vagabond Bay to sail the rest of the plane of water, returning to it as your safe haven and port back to your world. 

None of this need be easy. But it could be possible.

A Dreamland 

The Rainy City could also be a dreamland, a place that can only be visited in dreams. Your players could be drawn there, for a time, and have to find a way to escape this dreamland. Or maybe they choose to go there to steal dream magic from the wizards of the Tower Cliffs. Maybe it’s the dream of a vast and powerful wizard, and the wizard has some secret hidden away in here, a secret the PCs really want to get their hands on. Maybe other factions are sending agents in at the same time, seeking this secret.

Hell

Nine Swells, Nine Hells. Funny coincidence, that. And now that you mention it, you have to cross a body of water to get here. And once you arrive, you can’t go back. And the place is full of ghosts and demons, in addition to a lot of people, none of whom, now that you mention it, seem to have the most morally upstanding of characters. And hey, no elves. Is that because elves don’t have souls? 

Hm. Maybe hell is just very, very wet, and you’re in it.

Maybe the material component of a Raise Dead or Resurrection spell in your campaign could be… sail to the Rainy City, find your friend, remind them who they are, and get them out. Make an adventure out of it. 

Demiplane of Dread

I’ll leave it to you to figure out or decide who the dark lord is who is the master of the place.

The Distant Future

This assumes that the first model I presented is true — that the Rainy City is the city at the end of all worlds.

But your world isn’t flooding.

Yet.

And it might not flood for… a long time. Your PCs can visit the Rainy City in the distant future through time magic. This may be the future, but it’s not a future that affects their lives and homes directly. They could travel here for some purpose, have adventures, and return home. Sure, they know that the future is very wet. But it’s a long way off.

The Near Future

Or maybe it isn’t a long way off. Maybe Wet Doom is right on your doorstep. The end of the world is nigh. The PCs might travel to the Rainy City to try to figure out what caused the floods so they can go back to their own time and stop this all before it’s too late. 

A Rainy Coastal City in Your World

If it’s a magical world, which I assume it is if you’re thinking about adding the Rainy City to it, you can also just have it be a cursed port island where it always rains. It doesn’t even have to be that far off the coast, and it doesn’t even have to be that hard to get to, in this model. It should still see waves of refugees, but there’s always a war or invading evil army or something to flee.

This doesn’t exhaust the possibilities, but it should give you a sense of the range of options you have to drop this place into an existing campaign world, if you’d prefer doing so to using it as the sole home of an entire campaign.

Whatever you do, my invitation remains the same. Make the Rainy City your own.