Item description:

Go to the right and climb over the items and the broken gate
Go through the door/gate in the fence
Stand below the left ladders, hold L1 or R1 to active wings,
then press O to jump up, climb the ladders,
then jump over to the next ones on the right

Go up to the top and when you're standing on the platform,
hold L1 or R1 to activate wings, hold O (for long jump) to your left

Drop down to the next 2 platforms (the memento is on the 2nd one),
just press X when you are prompt to pick it up