There are 15 Trico Holes in The Last Guardian. Finding all unlocks the “Collar” Trophy (Bronze). Trico can put his head through certain holes in the game world. This happens when you go through a hole and there’s no way for Trico to follow. He will then stick his head through a hole to see where you are going.
You can do this over multiple playthroughs. Don’t worry if you miss one, all your collectible progress carries over into the next playthrough. If you miss one you can collect it in the next playthrough. No need to find all of them again, just the one you are missing will be enough to get the trophy. If you die or restart checkpoints you have to collect the hole again.
All Hole Locations
After going outside for the first time. After the stone pillar crashes down.
From the last two holes you must climb up the room with Trico’s help. Up there is a barrel in a small cave. Stand in the cave until Trico puts his head in it.
After first antenna room. Let Trico put his head in the hallway (where the first suits of armor spawned).
Holes #5, 6, 7
Just after first antenna room you come to an area with a smoking keg. Let Trico put his head through all 3 holes leading to the keg room.
Holes #8, 9, 10, 11, 12, 13
This is quite a bit later, after the next room with a green keg. After pushing the keg you fall into a pool of water. Climb back up you’ll soon reach the area with the last six holes (3 on each side). Just stand on the balcony outside and wait for Trico to put his head through them all.
Hole #14 (not needed for trophy)
In the mines after second antenna room. Cannot be missed (you need to jump on Trico’s head to progress further in the mines).
Hole #15 (not needed for trophy)
Again in the mines, this is story-related and unmissable. It’s the last hole.