It is a very basic question, but I am an amateur learning physics on my own, and it would help me if physics folks could confirm this. It seems like length contraction works in favor of the traveller. So if we could invent a mechanism to travel close to the velocity of light (or if a civilization in a different sun does it), we can trade the travel time for energy. For example, at 0.9c, the length contracts to about half, and energy need doubles, requiring only half the time. You could travel any distance in an arbitrarily smaller time if you could accelerate closer and closer to the speed of light and could feed the increased energy required for it.

While humans going at this speed is obviously unrealistic, I was thinking that civilizations closer to the blackholes could maybe use them to get slingshotted at higher speeds.

Did I get it right?