Hi there and welcome to my first guide. I bought Dust: An Elysian Tail when it first came out on Steam. I played through on normal difficulty first, up to 106% completion. I've just finished a hardcore playthrough and have reached 116% completion so far, and have earned all of the achievements. I love the game and felt like making a guide or two to share some of my knowledge and help out anyone who may need it.

Cages contain friends that need your help to become free. Each cage has 4 locks on them, thus requiring 4 keys to free the friend within. Every time you free a friend, you gain a +5% increase to your overall health. The friend will then appear in Sanctuary. You can rescue up to 12 friends, and after doing so, you should head on over to Sanctuary and check out how your buddies are doing.

Cages can be found in the oddest of places. Some may need a special ability to reach it, requiring you to backtrack once you have that ability. Some may be able to be reached by a little cleverness, even if you don't have the needed ability.

Locations and abilities/items needed:

The Glade: 1 cage.
Abadis Forest: 2 cages. Need sliding ability for one.
Archer's Pass: 1 cage. Need all resonance stones.
Aurora Village: 1 cage.
Cirromon Caverns: 2 cages. Need sliding ability for one, boost jump helps for the other.
The Sorrowing Meadow. 2 cages. Iron grip/vine climbing ability helps for one.
Blackmoor Mountains: 2 cages. Need the red orb for one, double jump ability helps for the other.
Everdawn Basin: 1 cage. Need the boost jump ability.

I feel that it's much easier to explain how to find them in a video, so here's one I made for this guide. Time stamps are in the youtube description, if you want to skip around to specific areas and such.