Cross through the next corridor, bomb or blast the crumbling blocks in the walls to crawl through the gaps, and watch out for enemies. Past the walls you'll find a room filled with sand, shoot the sand blocks to get through an head through the opening on the right. Drop down the next shaft to find a Metroid shell at the bottom with two openings leading left and right. Jump across the platforms in the corridor on the right, beyond here you'll find another Alpha Metroid.
Once you've dealt with it, go back to the shaft with the Metroid shell and head left. Drop down the next identical shaft to find another shell at the bottom. In the corridor on the right you'll find the former owner of the shell - another Alpha Metroid. Once it's gone head back to the shaft and go left. In this next room beyond another corridor you'll find yet another Alpha Metroid, but once you destroy it an earthquake will occur, lowering the lava way back in the upper cavern.
Journey back to the large cavern and sure enough - all the lava's gone. You'll know once you're back in the right cavern as the music will revert back to the main theme. Drop down the cavern while avoiding the spike enemies, you'll eventually find a hole at the base of the cavern, drop down and head down the next shaft. The path will slowly lead right, so continue following it. In the next cavern, drop down to find another area filled with lava, so it's time to go Metroid hunting.
Crawl through the narrow tunnel on the left to find yourself in the lower part of a familiar cavern. Go left to find a shaft leading up. Climb to the top and go left. In the next corridor, jump over the floating creatures above the sand, if you stand on them they'll fly downward. In the next cavern you'll face another Alpha Metroid. Once it's fried head left to find the second massive cavern containing ancient ruins - it's time to find more items.
Enter the ruins and save the game at the Save station. Go through the next corridor, but watch out for the gun turret positioned on the ground at the far left end. Go through to find another corridor with a Save station, go left to emerge back outside the ruins. Head left until you find an opening in the ground ahead, then drop down into the water below. Go right past the Metroid shell to find a shaft filled with water.
You can find a Missile Pod in the upper right corner, once you've found it drop down to the bottom of the shaft. Go right to find a corridor containing an Alpha Metroid, once you've blasted it go up to the shaft on the right and use the Spider Ball to climb up the narrow shaft. Once at the top, head left and blow open the door there with missiles. Inside you'll find a Chozo Statue holding nothing, so blow open a hidden hole near the door and drop down into the small room below the statue. In the top left corner of the small room is a hidden passage, use the Spider Ball to crawl through.
You'll find a room filled with balls the Chozo Statues hold, but the one in the corner between the two blocks is the one you're after. Bomb all the balls and blast open the one between the blocks to reveal the Varia Suit.
Once you've snagged the Varia, head back up to the ruins. Go left to find a shaft leading up and down. Drop down to the bottom and go right. Go down to the bottom of the next shaft to find a Metroid shell. Head right through the next corridor to find another Alpha Metroid, but this time you'll witness it evolve into a Gamma Metroid. Watch out for the lightning bolts it wields, just pound it with Missiles to finish it off.
Once it's dead head back to the shaft and go left. In the next corridor you'll face an Alpha Metroid, head left once you've dealt with it. Drop down the next shaft to find yet another Metroid shell. Down the right corridor you'll find an Alpha Metroid past a room filled with sand. Down the left opening you'll find another room filled with sand, a Gamma Metroid will be waiting on the far left. If you're low on health, go into the room on the left after you've dealt with the Gamma Metroid to find an energy refill ball.