Wieliczka is a salt mine a few kilometres from Kraków, worked for seven centuries, where the miners carved churches out of the rock they were digging. You come out a hundred metres down into St Kinga's Chapel, a full church 54 metres long and 12 high. The floor is rock salt, and so are the altars, the relief of the Last Supper along the wall, and the chandeliers hanging over it. Three miners cut it with the mine's ordinary tools between 1896 and 1963, none of them trained as sculptors. It is still a working church: Mass is said there, couples marry in it, and the salt walls give a concert an acoustic nobody designed. Kinga was a Hungarian princess who threw her engagement ring into a salt mine at home before marrying into Poland. The story goes that the first block of salt split open here had the ring inside, and she is the patron saint of Polish miners.
The carved halls are a sliver of the place. Nearly 300 kilometres of passages run under the town, most of them plain and cramped: timber-lined corridors you walk with old ore-cart tracks down the middle. You pass the foot of a shaft braced entirely in stacked timber, log crossed over log with no metal in it, the way the rock was held open in the early centuries. Elsewhere salt crystals bristle from the ceilings over your head like frost, built where salt-laden moisture dries on the rock, a little at a time over centuries, with no miner's hand in it. Salt dissolves, and that has been the danger. Ventilation put in during the nineteenth century drew damp air through the mine and began taking the carvings apart, until a dehumidifying plant steadied it. Since the 1960s one chamber 135 metres down has held hospital beds: the salt aerosol and the near-absence of dust and pollen treat asthma, so patients stay for days, breathing the air that was eating the chapels.