NieR: Automata's 3C3C1D119440927 DLC unlocks three challenging Colosseums. After receiving the Mysterious Letter, you'll need to locate these arenas to unlock unique rewards. Here's a guide to their locations:
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Trial of the Sand Colosseum Location
This Colosseum is situated in the desert. From the Desert: Center access point, look to the right (facing the direction you entered from) for an orange diamond-shaped structure. A machine guards the entrance, but it poses no threat. Completing this Colosseum to Rank S rewards the Destroyer Outfit (A2).
Gambler's Colosseum Location
Located in the Flooded City, access this Colosseum from the Flooded City: Coast access point. Follow the path towards the coast (the same path used to guard 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 gain access. Completing this Colosseum to Rank S rewards the Revealing Outfit (2B).
Underground Colosseum Location
9S ONLY: 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 enter the Underground Colosseum. Completing this Colosseum to Rank S rewards the Young Man's Outfit (9S).
