Warp Zone Cannons

ign.com:

In some worlds, there are cannons you can access (usually through taking secret exits). When you enter the cannon area, there will be a large cannon in the area, and a world number written below it. If you want to warp, simply drop into the cannon and off you go! Here is a list of the known warp zones thus far:

World 5 Warp #1: Take the secret exit from the World 1 Tower.

World 5 Warp #2: Take the secret exit from Stage 2-A.

World 6 Warp: Take the secret exit from the World 3 Ghost House.

World 7 Warp: Take the secret exit from the World 4 Ghost House.

World 8 Warp: Take the secret exit from the World 5 Ghost House.

Warp from World 5 to World 8

about.com:

Enter the World 5 Ghost House and get a Mushroom from the blocks. Then, go up the stairs untill you get to a place with three brick blocks on the left side of the screen. Stand on top of them and jump to reveal three invisible blocks. Next, wall jump on the left side to get on top of them. Stand on the middle raised block and duck, then jump to reveal a block with a vine in it. Climb up the vine and a Boxing Ghost will appear. Jump off the vine to avoid taking damage from it. Kill it and climb back up, and enter the door. Kill the two Walking Pumpkins and stand in the middle. The platform will wobble and as long as you stay in the center you should be fine. When it reaches the top, exit and jump on the flag pole. A path will open to the Warp Cannon on the World Map. Enter and use the Cannon to get to World 8.