Minute Physics has put together this viral video of what traveling through the center of the Earth would be if it was hollow. Near the center of the Earth, there is almost no gravity so you would end up floating around for a while. The furthest we have dug into the Earth is 12 km. by a Russian drill, which is only 2/3rd the size of Manhattan. They had to stop because it got too hot (180-degrees Celsius). You can just dig a hole through the Earth because the middle of the Earth is just way too hot.