Time dilation: At a constant acceleration of 1g, 100k galactic time reduces to 12 years ship time. Cf the link provided in the comment you're replying to.
As you approach the speed of light, the time observed by the traveler ticks slower, so you can travel vast distances in short observed time periods. So the people on the ship would spend 12 years, a manageable time period, but us more or less stationary observers would still see 100000 years pass.