Plane of Earth

Earth symbolizes stability, rigidity, stern resolve, and tradition. The plane's position opposite the Plane of Air in the ring of the Elemental Planes reflects its opposition to almost everything air represents.
The Plane of Earth is a chain of mountains rising higher than any mountain range in the Material Plane. It has no sun of its own, and no air surrounds the peaks of its highest mountains. Most visitors to the plane arrive by way of caves and caverns that honeycomb the mountains.
The largest cavern beneath the mountains, called the Great Dismal Delve or the Sevenfold Mazework, is home to the capital city of the dao, the City of Jewels. The dao take great pride in their wealth and send teams of slaves across the plane in search of new veins of ore and gemstones to exploit. Thanks to their efforts, every building and significant object in the city is made from precious stones and metals, including the slender gemstone-inlaid spires that top most buildings. The city is protected by a powerful spell that alerts the entire dao population if a visitor steals even a single stone. Theft is punishable by death, with punishment extending to the thief's relatives.
The mountains nearest the Fountains of Creation (on the Plane of Fire) are called the Furnaces. Lava seeps through their caverns, and the air reeks of sulfur. The dao have great forges and smelting furnaces here to process their ores and shape their precious metals. 
The border region between the planes of Water and Earth is a horrid swamp where twisted, gnarled trees and thick, stinging vines grow from the dense muck and slime.  Here and there within the Swamp of Oblivion (also called the Plane of Ooze), stagnant lakes and pools play host to thickets of weeds and monstrous swarms of mosquitoes. The few settlements here consist of wooden structures suspended above the muck. Most are built on platforms between trees, but a few stand on stilts  driven deep into the muck. No solid earth underlies the mud of the swamp, so houses built on poles eventually sink down into it.
It is said that any object cast into the Swamp of Oblivion can't be found again for at least a century. Now and then, a desperate soul casts an artifact of power into this place, removing it from the multiverse for a time. The promise of powerful magic lures adventurers to brave the monstrous insects and hags of the swamp in search of  these treasures.
The region of the plane nearest the Swamp of Oblivion is called the Mud Hills. Landslides constantly wear away the slopes of the hills, sending cascades of earth and stone  into the bottomless swamp. The Plane of Earth seems to constantly regenerate the land, pushing new hills up as the old ones erode to nothing.

Type

Dimensional plane