Ba'al maintained an outpost that was a secret test facility for weapons technology and gravity field generators, where gravity manipulation was used within prison cells and for torture. When O'Neill was captured and tortured by Ba'al, he was kept in a gravity cell which relied on the redirection of gravity to prevent escape. The secret outpost was destroyed by Yu, allowing O'Neill to escape when the artificial gravity generators failed.
Cross Reference: Anti-Gravity, Ba'al, Shallan, Tal'vak Acid
Episode Reference: Abyss