You know how Tylo is nearly the same size and mass as Kerbin. It's tricky to land on, and takes a little bit of planning. Now, hypothetically, let's say in our own solar system we had something like that. Same mass as earth, same size, gravity, but no atmosphere. If we wanted to land someone on that world, what would a lander for something like that look like? I am sure it would be far more complicated than the Lunar Landers used in the Apollo program and probably much larger too.