Altars in Shadow of the Colossus Shadow of the Colossus Guide, walkthrough

Altars become available after defeating the first colossus on any difficulty level. You can find 25 of them in different areas of the map. Each altar allows you to pray (press R2 when standing before a shiny wall) to regenerate your health and strength and to save your current location - if you'll die while exploring the nearby areas, you won't be taken to the starting location.

The altar not far from colossus 12 can be easily skipped

The map at the beginning of the chapter shows the locations of all altars found in the game. Visit and pray at all of them to unlock a trophy (Seeking Salvation). This trophy can only be unlocked after beating the game (i.e. defeating 15 colossi), as the final altar is located beyond the passageway to the final, 16th boss.