Along the Great River
This is a campaign for D&D 5e.
The world is centered around a mighty river which flows from the frozen north to the tropical south. There are a number of tributaries to the river, which flow into it from both the west and the east. Civilization is largely centered on its banks, within the temperate zone. To the east, civilized farmland rapidly gives way to dense forest. To the north, there is boreal forest and tundra. To the south the river enters a swamp that has so far proven impassible. And to the west the farmland slowly gives way to vast plains inhabited by nomads.