Lihzahrd Chest

Each of these holds a power cell, and that is the reason to clear the temple methodically instead of tunneling straight to the boss room. Cells are the fuel for Golem attempts and a failed attempt burns one, so a full sweep buys you a stack of tries before you have to come back. Do the sweep first, fight second.

Alongside the cells you can pull the temple's own furnace and solar tablet material. The finished tablet is the interesting find, since it lets you start a Solar Eclipse whenever you want rather than waiting on the weather roll, and eclipses are where several strong midgame weapons live. Fragments turn up often enough that even a run with no complete tablet usually leaves you close to assembling one.

Everything else is ordinary deep-cave chest filler. Nothing in that layer is worth going back for.