NieR: Automata's 3C3C1D119440927 DLC unlocks three challenging Colosseums. After receiving the Mysterious Letter, you'll need to locate these arenas to earn unique rewards. Each Colosseum features six ranks of progressively difficult enemies.
Colosseum Locations in NieR: Automata
1. Trial of the Sand Colosseum:
Located in the desert. From the "Desert: Center" access point, look to the right (facing the desert entrance) for an orange diamond marking its location. A machine guards the entrance, but it poses no significant threat. Completing Rank S rewards the Destroyer Outfit (A2).
2. Gambler's Colosseum:
Found in the Flooded City. Begin at the "Flooded City: Coast" access point. Follow the path towards the coast (the same route used to protect the resource ship). At the end, locate a waterfall to the right. Circle around the building to the left of the waterfall to find a Resistance member guarding the entrance. Bribe him with 1,000 G to enter. Completing Rank S unlocks the Revealing Outfit (2B).
3. Underground Colosseum:
This Colosseum is accessible only when playing as 9S. Start at the "Forest Zone: Center" access point. Follow the left edge of the forest until you find machines training near a large waterfall. Pass through the waterfall to access the Colosseum. Completing Rank S rewards the Young Man's Outfit (9S).
This guide provides the locations of all three Colosseums within the 3C3C1D119440927 DLC. Remember to complete Rank S in each for the best rewards.