Search the caves for hidden treasure

Search the caves for hidden treasure is an optional mission in Ratchet & Clank, in the Tobruk Crater on Novalis. This provides a reward in holocards if completed.

Walkthrough
Behind the ship upon is a small canyon with a pool of water which, when crossed, leads to a larger pool of water. You can swim in the water by holding to dive and swim down, and  to surface and swim up. Dive below and swim down to hit the exploding crates and immediately surface to destroy crates below and collect bolts, though do not swim below for too long or you will die when your oxygen gauge empties. Jump to the grassy surface with a bolt crank and turn it to open the door and enter a tunnel.

In the tunnel, jump up the rocky platforms to find amoeboids. These are small enemies which attack at melee range, though destroying larger amoeboids simply splits them into two smaller forms. They are best defeated with the Combuster or Pyrocitor. Kill the amoeboids to find a larger pool of water. Dive below and swim through the tunnel, to rise on the other end. Here, you can jump up and drop down to find yourself in another cavern with more amoeboids, defeat them and to the left you will find a holocard set, and obtaining it completes the mission.

To return to your ship, head to the pool of water below at the end, dive, swim through the tunnel here, then step on the button to open a door and you will have returned to the starting area.