If we assume that the second Death Star is built similarly to the first one, it is no stretch that the first one is quite hollow. Lando flew the Millenium Falc

If we assume that the second Death Star is built similarly to the first one, it is no stretch that the first one is quite hollow. Lando flew the Millenium Falcon inside of the second Death Star (along with Wedge, who was in an X-Wing) and they ended up coming to a very large area within the Death Star before subsequently destroying it and racing to get out.