Once you've whacked the statue, head back out and make your way back up to the main rocky corridor. Go past the three Skree and keep going to the left end of the corridor. Activate the Morphing Ball and plant a bomb by the wall to blow open a hole.
Go through and head through the door there. Run down the long sloping corridor while blasting enemies, at the bottom you'll find Energy Tank no. 1 (Crateria). In the next shaft you'll find Zebesians that can't be damaged with your beam weapon, so just pummel them with Missiles.
Drop down to the bottom of the shaft, behind the purple door on the right you'll eventually reach the Statue room containing the entrance to Tourian, you can go take a gander now, but once you're ready go through the door on the left. Go through the next rocky corridor, at the far end you'll find another elevator leading down to Brinstar, so hop aboard.
Once you enter this thorny region of Brinstar, go down the shaft, blasting any enemies along the way. When you reach the first two doors facing each other, go through the left one to eventually find the Map room, you can also reach missile no. 3 (Brinstar) in the door on the right. A Save room is a little further down, you might want to consider saving the game now.
At the bottom of the shaft, the left door leads to a Missile Reload room, go through the right door when you're ready. You'll now be in a long purple corridor which has a nifty background with falling snowflakes. Whack all the enemies here and go over to the blocked-up wall on the right side. Bomb through the wall, then keep going and go through the door on the right side of the corridor.
You're now in a huge purple shaft, you'll find another boss room leading off from the top-right corner. Before you go up there, go down the shaft to find missiles no. 4 and 5 (Brinstar), as well as the Charge Beam. Once you've found everything, go up to the top of the shaft and save your game in the Save room in the top left corner.
Go through the top right corner door of the shaft to find a thorny corridor with large Keyhunters flying about. Shoot them with Missiles to finish them off, then go over to the right end of the corridor. Open up the door in the roof and go up to find Spore Spawn's room. Refer to the bosses guide to beat it.