The Great Ungeness Trench was an underwater valley located on the ocean-covered planet Mon Cala. Following the Battle of Dac City in 18 BBY, which resulted in the city's destruction, the Sith Lord Darth Vader descended into the trench, where he encountered a massive beast.
The initial depiction of the Great Ungeness Trench occurred within the pages of Darth Vader (2017) 15. This canon comic, released in 2018, was authored by Charles Soule with illustrations by Giuseppe Camuncoli.