I have two worlds of fantasy in which I have run games before. The oldest one is of my own design, but runs mauch as the old D&D camps were meant to look. The main area is a human nation running along a huge river system. The capital is called Riverdale, a good sized walled city set in the river delta several miles from the sea.
The River, yes, that is its name, begins in the mountains as run-off from several glaciers, trikling mostly southward thru several Dwarf controled passes and vallies until the now navigable stream turns east from the first human trading post. The River runs almost due east for several hundred miles with well watered hills to the south and a mostly unexplored desert to the north. Finally, The River turns southward again, and much like the Amazon, Begins a long journey to the sea. Lakes and swamp like areas abound along its multible banks as it winds a slow path thru a long and nearly flat valley.
The delta near the mouth span close to fifty miles both across and in depth. It is covered both in cotton and tobacco farms.
Riverdale itself was conquered many years ago by a powerful paladin who has now grown old. He has no known heir, which may cause problems in the near future. His rule extends all the way to the Bend, (where The River turns from east to south) and many miles to the east of the water into to what is known as the hill country. In the hills and beyond are several nations and kings going all the way past the southern reach of the mountains.
To the east of The River, however is a wall. It is a sudden uplift in the earth that stands like a cliff, almost striaght running parallel to The River from the sea to the bend. The top of these cliffs are the Highlands, very little explored and known to be inhabited by feirce tribes.