High Fall is simple. Just jump off the top, avoid the iron bars, and splash into the water at the bottom. But if you just as much touch a bar on the way down you will die.

Good Luck!

Additional Notes

If you die you will spawn on the 5th layer instead of the top. I don't know why this in. maybe because the top block is the highest you can go. All you have to do is switch to creative mode to get back up. Same if you live.