It was designed to destroy all mermaids across the world by combining the trident and the full moon to absorb power from the Moon Pool and subsequently every mermaid's life. The merman who built the chamber fell in love with a mermaid and decided not to activate it, and instead found ways to invoke peace and stop the war once and for all. Since only a member of that merman's bloodline could activate the chamber, no other merman had been able to use it since then, and it became a lost ruin.