Guide in progress:
Blood Tower- After activating a switch, an elevator will activate. Go back to the elevator and keep an eye out on the right wall as you ascend for another switch. Activating this switch opens up a piece of the left wall of your elevator shaft. Enter that area and go all the way to the left. This will spawn a super strong beholder. Keep your distance as best you can and knock all of his projectiles back at him. Once he is dead, a chest will spawn and you'll have your first piece.
Highlands- You will reach a point near the end where you enter an underground section. Jump down and progress left, undoing over the crush trap buttons and dispatching enemies and a fire breathing gargoyle statue. You will have to drop down again where you can go left or right. Go to the left to find the (not very) secret area and dispatch the clawed enemy Guardian that arrives with counter attacks. This enemy will dig underground and try to hurt you from underneath, so get moving when you see he is about to emerge. After he is dead, collect your prize and continue to the right to fight to your next checkpoint.