Looking back at my past campaigns, the ones I've had the most fun running (and which were arguably the most successful) were the ones where the PCs could take a fairly sandboxy approach to exploring a wilderness region. I'd like to develop a new campaign like this again one day, but what I could use for such a campaign is an interesting premise. I am ruling the following premises out:
- Adventurers plundering old ruins for profit: Too trite.
- Adenturer-archeologists uncovering the deep history of the region for academic bragging rights: A lot of fun, but I have done this before.
- Making the region "safe" for colonization and settlement: While the whole concept of "colonizing the frontier" provides plenty of interesting background drama for a campaign that I don't mind exploring, it is too ethically dubious to make the PCs take the side of the colonizers by default.
So, what other premises can you come up with that provide a justification for player characters to hang around a frontier region and explore it?
I think there's a lot of space with fantasy and magic to handwave away a lot of the the ethical ickyness of colonization.
Completely off the top of my head:
You could have some part of the world protected by a magic shield. Many thousands of years ago some major player country in the world just magically closed their doors to the world. No one has been in or out since, and a lot of details have been lost to time.
Scholars have studied "the wall" for ages, and it's clear that something is changing. Many believe that whatever force has maintained it is running out.
Various world powers have begun stationing military camps outside of it, no one knowing what lurks inside or what might come out. Fear of the unknown. Tensions are high.
Some more enterprising folks are making plans to try and exploit what will be sudden access to unknown land, resources, and perhaps riches.
The players could have been hired by some research organization to discover what happened to this ancient civilization. Are they still around as a society isolated for millenia? Are they gone? How was "the wall" made and how was it maintained? Any information will pay, and having it first pays more.
Or they could be hired by a group intending to settle the new area, as a greed thing or because some group of people are being displaced by a large military force and need somewhere else to settle. Could have some plot about keeping traditions in unknown and different environs, and trying to mesh ancient technology with their lives.
Small holes start appearing temporarily in "the wall", but too high up to access and they close too fast to get in or out. Whoever hired the players believes they've identified where the first (or one of the first) ground level one(s) will appear, and that they can hold it for long enough to send the players through.
Could go in a lot of different directions with that, and you could have some distinct "phases" to the plot.
Maybe the players are the first in, maybe they aren't. As time progresses others may get in with differing goals. Other researchers with different focuses, settlers, people running into this new space to escape outside things, smugglers trying to make/find new routes, thieves and plunderers trying to score, greedy land barons trying to take over by being one of the first to make a settled foothold.
Options for how you handle the civilization inside too. Are they gone due to some magic shenanigans like Elder Scrolls Dwemer? Did they pass away in isolation? Are they strong and ready to rejoin the world? Looking to do conquest? Scattered survivors of a fallen isolated empire?
As a big change, the wall can fall completely a certain amount of time in and now there's all of that plus militaries and other larger forces scrambling around.
But I think the colonizer ick can be sidestepped with having the players supporting displaced peoples seeking refuge in a space that was previously inaccessible due to magic bullshittery.