From Halopedia, the Halo wiki
Acheron Fossae, Mars
Acheron Trauma Sim, testing site of numerous GEN2 variants.
Gdynia is a city located in the Acheron Fossae on Mars. The city is the location of the Acheron Trauma Sim, the testing site of several Acheron Security MJOLNIR Powered Assault Armor (GEN2) suits.
Gdynia takes its name from the real-world city of Gdynia, Poland.