My first PS campaign

That would be Nifleheim, the 2nd layer of the Waste. I recently sent my players there to the base of the tree, narrowly avoiding Nidhogg.

While not associated with the World Tree there, I also had a gigantic clock on the layer of Oinos called the Oblivion Compass or The Clock. I think I may have posted the description of that here on the boards somewhere (and definately over on WotC's boards). If that gives some ideas, feel free to use. Otherwise I might post some more ideas here tommorow.

The Oblivion Compass:
Location: Gray Waste, 3rd layer, Pluton

Dotting the hinterlands of the Waste are many a number of strange, enigmatic, and unexplained sites and ruins. Some of them are perhaps best left unexplained for what they might forshadow.

The Oblivion Compass occupies a broad, shallow valley roughly 3 miles in diameter. Filling most of the shallow bowl in the land is a gigantic series of cogs, gears, and other clockwork machinery jutting up from the sterile, ash strewn soil.

The name of the device, The Oblivion Compass, has been used by both the Night Hags and the Yugoloths for as long as records on the site have existed, though the Hags refuse to approach the place and the Yugoloths have an odd mixture of fiendish delight and a subtle undercurrent of fear when asked about it and its history.

To an observer standing at the rim of the valley that holds the massive device, it resembles not so much a compass, but almost a clock with multiple hands and no apparent markings for minutes or hours. Several of the dozen and a half hands are the same size, but made of seemingly different colored metals, ranging from silver, green steel, iron, copper, bronze, gold, and other unknown exotics. Other hands are inscribed with runes in no known language. The underlying clockwork is uniformly as gray and wasted as the plane surrounding it.

One of the hands of the device however is considerable larger and seems to function independant of the others, spinning at random, much like a compass needle. However no known landmarks upon the layer of Pluton correspond to any common point that the hand might gravitate towards.

The gears and associated clockwork are tarnished and rusted, but apparently still functional and the machinary spins and rotates with mad abandon at times, sending vibrations through the ground that are palpable for miles around and filling the area with the sounds of grinding metal on metal, the hollow tick of the massive gears in motion and a sense of malign dread above and over the typical sapping hopelessness of the Waste. At other times the compass grinds to a quiescent standstill and the normal conditions of the waste seep back into the region.

The gears appear like something ripped from the very heart of Mechanus, and some have speculated that indeed this may very well be the case. Recent findings by scholars of the Planewalkers guild have found more evidence for this, beyond simply the appearance of clockwork on such a massive scale.

Supposedly buried within one of the underlying and supporting sets of clockwork machinery examined by the group they found what they could only describe as massive gears and a flywheel seemingly constructed from the "fossilized bodies and broken limbs of modrons". They also noted, before being driven from the site by the threat of an approaching army of Yugoloths and Baatezu in transit to the city of Center, that the modrons all appeared to have expressions of absolute terror upon their faces. Lost was the normal logical, emotionless serenity of a typical modron, replaced with expressions of dread, pain, and horror.

Other travelers to the location have alternately described the "weeping shade of a Parai" seated upon a still hand of the device and the string of broken and mutilated Inevitables apparently welded onto the surface of a spinning gear rising from the tangle of underlying clockwork that supports the compass.

Perhaps the most striking tale, and the least substantiated, are stories that at the core of several of the main gears lies the still beating heart of a Secundus modron. However as all 4 Secundus Modrons are still alive deep within Regulus on the plane of Machanus this is either incorrect, or very troubling. Dead modrons return to the modron energy pool to be almost instantly ressurrected. A living modron heart would indicate that at one point the conclave of Secundus Modrons numbered one more among their number. And to each Secundus is given authority over an equal share of the population of the modron hierarchy.

Harrowing indeed if true, and difficult to explain. Any modrons asked on the matter refer the questioner to an ever higher level of modron, and the request is usually buried in the modrons' legislative processes to where it is never answered in the lifetime of any single individual asking the question.

Another speculative tale relates the runes upon several of the hands of the Oblivion Compass to the runes upon the perhaps mythical Loadstones of Misery. The Loadstones are said to be three titanic blocks of stone, one to each layer of the Waste, that are themselves the driving force behind the emotional and spiritual leeching of the entire plane.

At times the runes upon the Loadstones glow red or blue, at which times the emotional leeching of the Waste either triples in intensity or reverses itself temporarily, and always the draw or reflux originates from the monolith itself.

Some have speculated that their creation is tied somehow to the city of Center and a speculated 4th Loadstone at its central point, and/or to the experiments and machinations of the Baernaloths.