Without the invisible walls, you can go as far as you want. At first you can just follow the road, flora quickly stops rendering, but you can still walk on.
The FOOMP, you fall through the ground into the 'ground water' below. Moving back magically poofs you back up though.
But you can 'reach' any piece of 'land mass' this way, but I wouldn't say it's worth the bother unless you're too bored to play, but not bored enough to quit
