Metroid Prime 2: Echoes/Gravity Boost

Torvus Bog
The next upgrade takes you to an underwater section of Torvus. The upgrade is used underwater, but since there aren't really any underwater areas outside Torvus, it's not as useful as you might hope.

Torvus Temple
Get to the lower part of Torvus Temple, and go through the Morph Ball tunnel opposite the Temple Access door. Blast open the Green door on the other side. You could have done this any time after getting the Super Missile but it was a dead end until now.

Underground Transport
Scan the control panel to activate the lift, and take it to the lower level.

Hydrodynamo Station
This is a large round room with a ledge around the middle and a deep pool in the center. Get a scan of the floating soccerball like creatures, they are called Preed and are this game's equivalent of Puffers, though in fact they are Space Pirate drones. Before diving into the water, hop up the platforms to the top of the central pillar and blast open the Missile door near the ceiling. If you fall in, locate the doors into the central pillar near the bottom to be fired to the top.

Save Station B
This is the only save station in this part of Torvus, so you'll want to return here fairly often.

Hydrodynamo Station (cont.)
Jump into the water and get to the lower ledge around the central pillar. If you fall to the very bottom then switch to Morph Ball and ride a current that flow up the outer wall to get to the next level up. Scan the large swimming creatures here. They're Bloggs and they appear often down here in several forms. The only time you can hurt them is when they're swimming straight at you with their jaws open, so it takes a bit of nerve to get a shot in.

Locate the scannable pillar on one of the side ledges on this level. Get around behind it and scan it to release one of the three locks attached to the central ledge. Get back to the center and use the Orb Cannon to fire yourself back to the top. As long as you're up here you might want to get a quick save in.