It was placed in an area mostly inhabited by humanoid races, orcs, goblins, hobgoblins, etc, a "nation" (very much in quotes) held together mostly by fear and intimidation of some very strong individuals.
The original thought that brought it on was pretty simple, resulting from a discussion between the psuedoDM's(providing creative input on the world design) and myself(primary DM and world architect). We were discussing the distinct lack of "just plain strange stuff" in our home-grown world, and began talking about things that might be considered "world-renowned" but not necessarily useful or anything.
We got to thinking about specific regions. One region, Kedion, is a large expanse that just happens to be an area of mostly crappy land(swamps, deserts, steppe, mountains, not really hospitable land), that the "evil critters" can have because nobody else wants it, so they do their thing there and nobody really bugs em.
What would be in that region? How about something that's just there, and nobody knows why... what could an orc or goblin realistically accomplish, what would stand the test of time from the mayhem and still be standing after a long time? A mountain? Ok, what makes it different? Maybe they carve it into something, like Mt Rushmore. Nah, too complicated for orcs and such. Well, maybe something simple but big and tough, thinking geometric shapes. Pyramid? Been there, done that. Sphere? A giant rolling mountain? Yeeeeah, not so much(***see below). Cylinder? Again with the rolling thing, but at least it would be in one direction. Square... hrm... ok, that might work...
We kinda got stuck at that point, thinking about why it would be done, how it would be done and so on, but then we got to thinking about how paleontologists(sp?) aren't sure how ancient peoples did a variety of things here on earth, and thought we didn't need a reason.
We were thinking, maybe it's just been there. Maybe orcs use it as a rite of passage or something, they climb to the top and light a ceremonial fire, or something, the area around the base being littered with skeletons of creatures that had tried the test and failed.
But beyond that, we were like... hrm... so, not so much adventuring potential, huh? And we left it like that.
*** About a rolling mountain... imagine a concept of stopping a rolling mountain before it crushes some thriving metropolis or something. That would be a somewhat interesting adventure, but again, it needs a bit of fleshing out before it becomes viable.