Interstellar Travel Could Be Possible Even Without Spaceships, Scientist Says

Still a spaceship, regardless of the building materials. Hauling a planetary mass, however, is far from practical. Ideally you'll try not to carry too much extra mass and planetary masses increase at a power of 3 while usable volume increases by a power of 2. You want something where the usable volume scales with the mass.

OTOH, if you can use the planet itself as reaction mass, then you can afford a lot more initial mass, but there won't be much of a planet left when you finish braking.

Let's find a civilization that has done this, observe their situation and then maybe we can give it a shot.