Anthe

"They call it the city of flowers, but the flowers are crystals, spiral matrices grown on the walls of Anthean caves. The inhabitants of Anthe are at least partly crystal too: they call it "going sharp." Becoming more perfect, and clearer, and colder."

Anthe is a strange city of crystal located under the Zee.

Ouch!

"The inhabitants of Anthe go sharp. Not all at once, but piece by piece, they turn to crystal. They sort themselves by sharpness, too: the sharp-handed cluster with others of their kind, ignoring the keen-footed and the brittle-waisted."

The people there are an odd lot who can turn parts of their bodies into crystal at will: skin, bones, lungs, spleen, and even genitalia, a process called Sharpening. These new organs can offer unique abilities to their users: crystal bones and skin can protect their "wearer" from taking too much environmental damage, and lungs and stomachs of stone offer unique resistance to poisons and toxins. The training rituals are quite brutal however, and Sharpening can lead to horrific body horror.

The Sharpest

"It is a cavern of giants. They were all at one time men or women or other creatures you might meet familiarly on a London street. But they are larger now, grown like oaks into the cavern floor. Their bodies are clear as lens-glass. Their faces are past the necessity of expression. They are your superiors, but you have come far enough that they are willing to help you if you wish."

The crystallization of the body also gives rise to a rigid caste system within the caves. Members of different walks of life (thieves, mercenaries, the occasional Clay Man) turn different parts of their bodies to crystal to enter certain caves or perform specific duties. However, one is not limited when it comes to how much of one's body can be turned to crystal: it is not uncommon for people to fully crystallize and become one with the cave after many years of residence. These beings are called the Sharpest.