The Pits of Hathsin are a system of caves near Luthadel on Scadrial in which Atium crystals grow. It is also a concentration camp of skaa set up by the Lord Ruler to mine the Atium crystals.
Allomancy cannot be used around the crystals, as they will shatter, so the imprisoned skaa have to mine it by hand. All skaa in the Pits have small scratches along their arms from the 'teeth' of the crystals. The Pits are looked after by House Venture. Each skaa has a week to find an atium geode; if they fail, they are beaten savagely to death.
Kelsier is the only known person to survive the pits. He was there with his wife Mare on account of sneaking around Kredik Shaw. She dies and he snaps and escapes.
Only days before the fall of the Final Empire, Kelsier returned to the Pits, destroying all the atium crystals he could find, and setting all the skaa prisoners free.
The Pits are also the location of the liquid form of Ruin, the counterpart to the Well of Ascension.[citation needed]