Cannon

There is another exit in the tower (red flag) that opens the path for the canon. First off, you need the blue turtle shell to use for this. So where the checkpoint is, there is a green tube that spits you up in the air where there are lots of coins (about 20, you go over and then they appear) in a straight line. So when you land, you must jump back down to your right where you see a door. Enter and there should be lotsa blocks that go in and out. Jump down to where the big coin was/is and stand by the door. Up in the right hand corner, when your timing is right, you should be able to walk through as if you were entering a new room. Just follow that and you'll eventually come to the red flag.