Inspired by some of Fates Warning's older tracks and albums, the following is a pitch I made to a publisher that was ONLY turned down because I don't want to learn 4th Edition (and frankly writing an adventure this short would bore me).
Part One: Witch Meadow Run
PCs must stop a druidic ceremony and/or witch coven that intend to summon a great treant or earth elemental to wreak havoc on the civilized world (they put nature first etc). Lots of intrique and timing. All about finding out what's going on and where. No as much combat, I suspect, as normal. And no direct line to the ending.
Part Two: Giant's Lore
The PCs having thwarted the witches, have a bigger problem now. A giant, living under the earth, has been roused by the start of the ceremony. Having been asleep for centuries, he is angry, and hungry. Playing upon the traditional fairy-tale giants, he is merciless and has no allegiance to anyone — killing orcs and elves alike.
The adventure is much different than the first act. In this one, opportunists and victims abound as the PCs wade through the dark forest, in an attempt to stop the rampaging giant. Every turn is another unexpected encounter with someone who has either suffered because of the giant or a jerk who intends to take advantage of the chaos (orc warlord who expands his territory, dark elf commander who kills his brother, druids who try to direct the giant toward the cities, etc.)
Eventually, the PCs come face to face with the giant, unsure of what, if anything they can do to stop this juggernaut (it is beyond their power level, purposely). The interesting conclusion here is that the PCs must fail (maybe even die). If you know anything about the three-act structure, this is exactly what's supposed to happen. Which is fine, because in the third act…
Part Three: Awaken the Guardian
… the PCs must complete the very ritual they tried to stop, summoning the earth elemental, this time to destroy the giant... If necessary, they must go to another plane of existence altogether (especially if they died).
However, the elemental cannot do it alone and the PCs must complete other tasks, all the while, while the armageddon clock ticks down (metaphorically).
The structure of the three adventures plays upon the themes CHAOS/NEUTRALITY/LAW. In the first part, druids and/or witches work in consort (good and evil) to destroy a city (law), a very chaotic, but not necessarily an evil act.
In part two, the giant is neither good nor evil, lawful or chaotic. He serves himself, almost like a force of nature. Those encountered, come from every walk of life (in fact, eight key encounters to illustrate this point wouldn't hurt).
Finally, in the third part, the PCs must restore law and order (they could ignore everything I guess), by destroying the giant using the mindless earth elemental to do their bidding.
I do not think I've seen this adventure done before and it certainly toys with players pre-conceived notions of structure.