You could visit a mining site and go down haha. How flat do the believers think the world is? Is it supposed to be 2 dimensional or are they saying its a few miles wide or what?
I actually never heard about how they think about the depth of earth.
@Batman: Can you dig "through" earth and fall off?
I think there's too much current flowing through the ground and temperature is too hot to penetrate that layer; imagine puncturing a can of molten rock and metal under high pressure that comes into contact with cold water. That's more than just falling off if you get through.