where is 8-7?

You have to get the secret exit in 8-2. The hint video at Peach's castle will unlock after you beat Bowser.

This page on our guide runs you through completing 8-2 and getting to the secret exit. There is a video for the level also:

http://www.supercheats.com/guides/new-super-mario-bros/star-coins-world-8-2

In world 8-2 you need to go past the halfway mark, upto the two pipes one red and one yellow jump on to the wall above these and you will come to a wheel turning thing on the first one go backwards into the wall and go throught the pipe throw the pow to get lots of coins

there is a secert exit on world 8 to get to it. you can watch it on peache's castlein world 1. but you have to buy it with star coins.

1. In 8-2, before the pipe to exit, go forward.
2. As you bump into the wall you find a secret area with the 3rd star coin.
3. Then go back. Leave the secret area and as you bump into the other wall you find another secret area with a pipe.
4. Go down, go forward until you find 2 pipes - red and yellow. I think it's the yellow - if not red.
5. Go down and you'll be outside. Try not to fall into the lava and go forward untill you find the red flagpole and jump on.
6. GONGRATULATIONS! On the map screen go up and you be on 8-7.
7. Press the button with the number "2" to play.

there is a secret cave with a pipe in it after the checkpoint in 8-2.