Shadow of the Colossus Unlockables

Finish the game and save when prompted after the credits. A new game can now be started in hard mode.

Finish the game and save when prompted after the credits. You will be give a bonus item for every two Colossi defeated in Time Attack mode. Under the normal difficulty setting, the following bonus items will be unlocked, in order:
Whistling Arrow: Distracts a Colossus.
Cloak of Force: Sword damages a Colossus more
Mask of Strength: Inflict greater wounds to a Colossus.
Lizard Detection Stone: Detects white tailed lizards.
Fruit Tree Map: Reveals the Fruit Trees on map.
Mask of Power: Inflict greater wounds to a Colossus.
Cloak of Deception: Invisible to a Colossus.
Flash Arrow: Explodes when hits Colossus.
Brown Horse: Hold Square to start game at the main menu to get a brown horse.

When playing Time Attack mode under hard difficulty, the following bonus items will be unlocked, in order:
Harpoon Of Thunder
Sword Of The Sun: Light beacon operates in patches of shadow.
Fruit Tree Map: Reveals the Fruit Trees on map.
Shaman's Cloak: Increase defense and lessen damage.
Lizard Detection Stone: Detects white tailed lizards.
Shaman's Mask: Increase defense.
Cloth Of Desperation: Parachute for safe landing
Queen's Sword From Ico

To unlock the 17th colossus, beat all 4 modes. Then, climb the outside of the temple to the secret garden. The 17th colossus will appear in a short cutscene like the other colossi, smashing the rear wall. After you fight him, the path to the very top of the temple will be opened, leding to a very "special" surprise.

Defeat all sixteen Colossi and unlock all items in Time Attack mode under the normal difficulty setting. Then, hold Square at the title screen.

Defeat all sixteen Colossi and unlock all items in Time Attack mode under hard difficulty. Then, hold Circle at the title screen.

Finish the game four times (all four modes) and get a large amount of stamina, Travel to the ends of the world and locate the patch of ivy on the northeast side of the shrine. Climb up the ivy and follow trail all the way up and around the ledge to the right. Jump across at the other end of the ledge to reach the next set of ivy. Continue on until you get to another ledge above that you must climb around. Once at the other side of this ledge, climb to the right then shimmy across another ledge that leads behind a column. Jump to the ivy-covered column, then continue climbing. The ivy will lead to a walkway. Climb the stairs and walkway to the left of the garden. REMEMBER: Eating fruit from the trees causes damage. You must defeat a seventeenth Colossus to continue to the end of the path to the top of the temple.

It is possible to reach the Secret Garden early. Find the patch of ivy behind the Temple you start at (almost directly under the huge bridge you came in on). If your grip meter is high enough, you can just jump straight up the side until you reach the first ledge, which has a small patch of leaves on it. Position yourself directly under that patch of leaves. Continue to hold Grip/Duck and jump straight up. Your character will immediately duck in those leaves, allowing you to refill any lost grip. Then, continue around and up the side until you reach the path leading to the garden.

Quickly press Left Analog-stick Down + X, Left Analog-stick Down + X.

Hold R1 + X.