You're getting closer to your goal, which lies at the heart of the Whirlwind Maze. Just walk along the path, making sure to get all the treasure. Especially important is the Neo-Bahamut materia, which, if missed, can never be found again. At some point, Tifa will insist on going with you, so if you havn't been using her, you might want to stop and gain a few levels. You shouldn't really have any problems here, except for the chasms with the gusts of wind. The trick is to wait for it to calm down so that you can pass through. The green stuff and the lightning are just there to annoy you--it's the regular wind you're really worried about here. (Btw, if you do run into a gust of wind and get thrown back, you are forced to fight a relativly easy enemy, who has the "White Wind" Enemy Skill if you havn't learned it yet.)
When you come toward the end of the line, you'll face probably one of the easiest bosses in the game, Jenova-DEATH. (If you protect yourself from fire, you'll be completely untouched). Give the Black Materia to Red XIII or Barret (doesn't make any difference), then play out the lengthy scene that follows. You'll see Sephiroth in his true form in a giant materia crystal. Cloud will give him the black materia, he will cast meteor, and The weapons will be unleashed upon the world. In theensuing chaos, Cloud will dissapear, and the rest of your party will escape, anlong with the shinra people, on the Highwind. You'll now be taken back to Junon.