Mechanus

From Manuel of the Planes (3e):

It is the plane of ultimate law.

It is where premeditated plans are born.

It is the gear works for the multiverse.

Mechanus is where perfectly regimented order reigns supreme. It consists of equal measures of light and dark, and equal proportions of heat and cold. It is as predictable as the drip of a water clock and as obvious as a tree in a field. On Mechanus all law is reflected in a single infinite realm of clockwork gears, all interlocked, all turning according to their own measure. The cogs seem to be engaged in a calculation so vast that no deity knows its purpose, except that it is somehow a function of law.

At first glance Mechanus seems as straightforward as anything on the Outer Planes. However, subtleties lurk just below the surface. Every kind of law can be found in the Clockwork Nirvana of Mechanus, from simple maxims to devilishly twisted rules of decorum. But for the most part, Mechanus contains no passion, illusion, or pain. When all consciousness is completely subsumed into the whole, perfection follows.

Mechanus is a single infinite plane without defined layers. The void is filled with gargantuan interlocking wheels, like the internal cogs of an ornately carved clock. Some connect at right angles, and others connect along a single plane. The wheels, also called cogs, are composed of stone, earth, and metal ores, as if a deity carved them from the mantle of the Material Plane.

Many of the cogs are more than a thousand miles across, and they turn so slowly that their rotation is imperceptible. Yet turn they do, as witnessed by much smaller island-sized cogs that interlock with the much larger wheels.

These smaller cogs seem to turn at an almost dizzying pace, although inhabitants feel no centripetal force once on the surface of a small cog. The objective directional gravity means that inhabitants won’t be spun off the edge of a cog unless they’re standing within 10 feet of the rim.

Vision is normal on Mechanus. The plane is lit by a white, all-encompassing light springing from the very void for 12 hours, and is dark for 12 hours. Hearing is also normal, though the bass rumbling of cog turning on cog is sometimes audible near the edge of a face.