Rhûn

When I was thinking of ideas for my creative project, one of the ideas I considered was to delve into the Rhûn area of Middle-earth, specifically the Sea of Rhûn area. The Sea of Rhûn area is near the Lonely Mountain and is never talked about in Tolkien lore other than seen on the maps. I am curious what happens in the Rhûn area and perhaps if Tolkien intended there to be anything happening in the area or not. I also wonder what the area is like and whether or not there are important artifacts left behind in the area similar to Moria or perhaps the dead marshes. There is so much potential in the unexplored region of Rhûn that I have a hard time deciding what might be the most likely.

The south of Mordor (Harad) is another area not talked about hardly at all in Tolkien's lore or at least I haven't read about it. These areas which are included in the legendarium but aren't talked about make me personally, more interested in the legendarium as a whole. Does anybody else wonder about theses areas of Middle-earth and has anyone tried to piece together a story/ history for these areas?