Here it is! Minor World 11!

In the Ruin with the Varia Suit go to the rooms that goes...Save Point, Autrack, Save Point. Head left until you are in the ascending room with Platforms and Tsumuri's. Go up and right and jump onto the wall above. Spider Ball upwards until you reach the room with the Spikes and Alpha Metroid. Kill the Alpha than go to the bottom, enter Morph Ball and head back and forth using the Start/Select Trick. A hole will open in the floor eventually. Go through into either a wall with a Missle Tank or the Minor World.