If you're mad enough to find all 79 well-hidden golden relics, you'll unlock a new area and a powerful sword that are totally unique to the PS4 remake.
Shadow of the Colossus - All 79 Relic (Coin) Locations, Secret Underground Area and Sword of Dormin
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Shadow of the Colossus - Where to Find all 79 Gold Coins
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Shadow of the Colossus - All 79 Relic (Coin) Locations, Secret Underground Area and Sword of Dormin