One of the last campaigns I made homebrew contained 2 countries on either side of a line of mountains. They were once part of a larger kingdom, but has fractured over the last few hundred years. They traded back and forth up to several years ago when the BBEG took over with his goblins and hobgoblin allies. Many of the locals were imprisoned and forced to labor in camps. This country became a brutal dictatorship and has sights on their neighbor on the other side of the mountain.
The PCs are from the kingdom on the safe side of the mountains along the coast. There was a few low-level adventures in the foothills where they eventually found a set of old tombs containing a portal to the other side of the mountains into another set of ruins. Some of the hobgoblins from the other side were guarding this and sending forays into the surrounding areas where they first encounter the PCs. Once the PCs cross over, they encounter a resistance movement and further adventures attacking the hobgoblin strike force, the goblin bikers riding worgs, and the ogre enforcers.
Eventually they start to uncover the undead threat at the top of the structure. There was a stone wagon being sent around the countryside containing death wights and they would leave a distinct message to farms and towns that were causing trouble. There was a floating earthmote being pulled by giant elephant types and ruled by one of the regional governors. Things led to a final conflict in the mountain pass with a great battle.
The pass was large enough for several adventures in the pass before the final battle. The pass was 15 miles long, 10 miles wide and had castles at each end. Part of the pass contained a shortcut, but ruled by a powerful mage who created constructs. They needed to parlay with this 3rd party to allow troop to pass through his lands and behind the goblin army. They also met with equally powerful forces from the bad guys meeting for the same thing. There was another old temple in the pass that contained a item needed for the battle as well. In the end things went well enough and the pcs were made rulers of the pass.
