Zoethall was founded in the Lith-Crillion Era by kuo-toans caught in the strong currents of the Sea Tunnel. They were sucked out of the Sea Tunnel by way of a whirlpool that works in the reverse, that is drawing water upward to the surface where it spills into lake Yatúrz. For a time, they eked out a miserable existence in partially submerged caves along the lake's western banks. Their hunters ended up finding a passage that goes into the bowels of the Underdak, a passage called Tumbo Gein. Where this passage becomes part of Vul Sahsir, they built the settlement Zoethall.
The deep gnomes of Zoethall are Qya-Qhar slaves or descendants of slaves. Some deep gnomes earn a quasi-freedom, but these are not normally good-natured people with such a mentality weeded out of them from generations of slavery; unless they escape, first generation slaves can never earn their freedom.