The Sea of Rhûn was a large landlocked body of water situated to the east of Rhovanion between a large forest and a range of hills. It served as the outflow for the River Running.

The area was known for its wines and it was said that the wines of Dorwinion, an area on the coast of the Sea of Rhun, were renowned even in Beleriand.

Although the area made its wealth through trade, it appeared that by the end of the Third Age trade was only maintained along the Running and its tributaries with the Wood-elves of Mirkwood, the men of Lake town and the dwarves of the Iron Hills.