Go to Spiral Mountain. Now, find the flight pad on the mountain in the middle and jump off of it. Fly above Banjo and Kazooie's house and try crashing into the cliffs above it that are supposed to set the boundaries. Eventually, you'll land on one and you can walk around... but you'll be blocked by an invisible wall. You can sort of check out the place by walking slowly so that you almost fall off but then grab onto the ledge. Then, you can make your way around the boundaries using the Grip Grab.
Submitted by: Mike