Metroid Prime 2: Echoes/Power Bomb

Torvus Bog
The next upgrade is in Torvus, but it's near areas you've already been to so there's not really any new exploration involved.

Main Hydrochamber
Get to the underwater part of Torvus and go to the Main Hydrochamber; this is where you fought the Alpha Blogg. Go through the doorway opposite where you picked up the Gravity Boost, then Spider up the track to a portal.

Undertemple (Dark side)
Drop down and enter the main part of the room to start a boss battle.

Spider up to the top of the structure and grab the Power Bomb. These clear Yellow doors and destroy Benzium, and there are lots of both scattered around the game. The main problem with them is keeping topped up ammo; you only get two to start and the game is pretty stingy about dropping refills.

Blast open the Yellow door near where you picked up the Power Bomb to get out of the room.

Undertemple Access
You can either get back to the Light side via the portal here, or continue back to the Undertemple Shaft.

Expansions (Torvus Bog)
There are plenty of new expansions to get now, and they're spread throughout the game. We'll cover the ones in Torvus and Agon here.

Gathering Hall
Go to the great hall; one way to get there is using the White door in the Hydrodynamo Station. You're going to need two Power Bombs for this so you might want to stock up ahead of time. Drop to the bottom of the pool and use a Power Bomb to break the glass floor. Now use another Power Bomb to break the plug underneath; this causes the water in the room to completely drain away. (Note that getting around here will be a bit different after this and you'll need to use the Grapple Beam to reach some parts of the room.) With the water gone, the floor is now a large half-pipe, so start boosting to reach one of the Spider Ball tracks on either side. Follow a short Spider Ball course until you jump directly into a bomb slot. Activate the slot, then do the same thing on the other side of the half-pipe.

With both slots activated, a force field over a high ledge disappears and a ledge leading to it come out of the wall. Go to the door to Transit Tunnel West and use the Grapple Beam to reach the new ledge. From there it's a quick jump to get a Missile Expansion.

Training Chamber
It's a short trip through Transit Tunnel West to reach the Training Chamber. Follow the Spider Ball track starting to the left of the Spinner; you have to do a couple jumps on the way. Drop down to a ledge in front of the statue when you reach the end, then activate the bomb slot there. The statue moves forward allowing you to reach a Missile Expansion.

Chances are you'll have collected a Power Bomb from the Bloggs here. If so, then Spider up the track behind the Missile Expansion and blow open the Yellow door there. This eventually leads to Sanctuary Fortress, but we're not going there yet.

Torvus Grove
Get to the upper section of Torvus and go to Torvus Grove. You'll need two Power Bombs for this so try to farm them on the way. Two of the tree trunks here, the mutated looking ones with thorns, have been weakened, so drop Power Bombs to destroy them and make the tree fall. It breaks open a wall so you can reach a Missile Expansion.

Great Bridge
Get to the Great Bridge; it probably doesn't matter much whether you go via Forgotten Bridge or Torvus Temple. If you're coming in from the Abandoned Worksite then you'll see a section of weakened rocks on the left as you enter. Otherwise, use the Orb Cannon to get to the bridge and notice a different section of weakened rocks at one end. Either way, use a Power Bomb to destroy the rocks and follow the tunnel; you'll get a Power Bomb Expansion inside. The tunnel connects the two sections of weakened rocks, so you can either continue to the other end or go back if you want to save a Power Bomb.