After you get the Charge Beam, you learn your new destination and head down to Norfair.

Reach Your Destination

Go down from the elevator and use bombs to the left or right of the metal barriers to break through the floor next to the barriers. Go through the door on the right and use the save room if you wish. You can optionally go into the room on the right, but you'll soon find that there is no way to proceed there right now, so instead, go left, through the save room, back to the entrance room, and then through the door on the left.

Infinite enemies will fly up from the pipes. They require two beam shots or one charged beam shot. To the left, flame enemies are walking on the platforms. Make your way to the left. You will see a Missile Tank up above, but you can't reach it yet.

Keep going to the left, then when you're blocked by a wall, use Morph Ball to bomb the base of that wall. Roll through the hidden tunnel and use another bomb to break open the other side.

To the left, jump up onto the top of the ledge and roll left through the tunnel. Then go left and go through the door at the end.

Go up, get on the elevator, and push up to go up to Crateria.