But unless you have a way of slowing down again you'll never see anything of your destination, just the briefest of flares of light as you sail past. And if you

But unless you have a way of slowing down again you'll never see anything of your destination, just the briefest of flares of light as you sail past. And if you do have a way that involves anything like physics that we recognise, you've brought along a huge rest mass that then got accelerated to near light speed. Probably your civilization needs to be approaching Kardashev Level 2 to pull this off.