Celeste

Turn on Assist Mode - Invincibility and infinite dash to make these achievements easy.

After you pass through the first locked door that needs a key, you'll get to the dark zone. In the middle of the the first large dark room, above your head, there's a room that holds a key. You'll want to get that key.

After you have it, drop down to the large dark room and continue right. In the room to the right when you find the first red blob, you'll see yellow lights on the wall. Directly above the second light past the blob there is an opening in the ceiling. Dash into that opening. This will take you past the locked door.

After you cross the big chasm, there's a small room with a dirt patch in the middle. Break that dirt patch and you'll find a locked door. Go through it to find the heart chamber.

If you have assist mode on, dash up above the door to find the heart. If you don't, you have to work your way counterclockwise around the room using the platforms and walls.