Metroid Prime/Morph Ball

By now the hint system should be pointing you to an unexplored section of the Chozo Ruins; this is the location of the next equipment upgrade.

Main Plaza
You may notice that Beetles now appear near the Nursery Access door and there are War Wasps near the bridge. In general, new enemies appear and occasionally disappear from certain areas when you get equipment upgrades.

Find the Missile Lock Door that was on the left when you first entered from the Ruins Entrance. (If you're coming from Nursery Access then go right, down the ledges, and it's the door on the right.) Fire a missile to blast it open and go in.

Ruined Shrine Access
There are two groups of Scarabs are in this room, clear them as in Nursery Access.

Ruined Shrine
This room is divided into two sections by a wall. There are ledges you can use to climb over the wall on one side, but once you drop into the far section there is no going back until you get the Morph Ball visible on the far side of this room. The upgrade is guarded of course so when you approach a battle begins.

Transport Access North
Go back to Transport Access North (the room behind the platform where you picked up the Missile Launcher. The path is a bit easier with the Morph Ball since you can just plow through Scarabs with little damage and you can roll under Plazmites. When you get there, switch to the Morph Ball and go through the hole in the far side of the room. The tunnel is just big enough for the Morph Ball to fit and it leads to a kind of vertical maze where you have to guide the Morph Ball through in side view. There are several of these mazes in the game and this one is relatively simple. Move the Morph Ball until you encounter a piston moving up and down, then ride the piston up to the next higher level like an elevator and move to the next piston. Go through the tunnel at the top level to come out at a door leading to the next room.

Transport to Magmoor Caverns North
This is a transport similar to the one use to go from Tallon Overworld and Chozo Ruins, but it leads to a dead end at the moment. There are two other doors here, but only the one on the right leads to anything useful now.

Vault Access
Follow the passage and switch to Morph Ball to ride the piston elevator to a tunnel. Switch back to normal when the tunnel ends to hop up some ledges, then switch to Morph Ball again an follow the next tunnel.

Vault
The vault for which this room is named in right in the middle and you can see a Missile Expansion inside. It's not reachable at the moment though so save it for later. Go around to the right of the vault and scan the inscription there, then continue to the door at the far side.

Plaza Access
This is a cave with glowing walls. A small group of Beetles attacks but they are easy to deal with. Follow the passage to the end.

Plaza
You're now on a ledge high above the Plaza. There is an Energy Tank here which you may have noticed before but there was no way reach it until now. Get the tank and drop down to the main level.