The Subterranean Caverns are the seventeenth level of the game. The Caverns take place underground. You walk on catwalks above water. There is a swirling ledge thats leads up to a room. There is also a hidden way to the outlet pump controls behind some lockers in an arms cache. The guards in the Caverns are Janus Special Forces and carry AR33s and ZMGs. You are required to get security cards for certain doors. At the end of the level you find Alec Trevelyan who's running from you. When you finally find Trevelyan, he runs to an elevator and escapes for the time being.