The Bowl of Heaven, by Gregory Benford and Larry Niven

Imagine if you will, a hemisphere 93 million miles in radius with a hole in the bottom and the sun in the center of said bowl.  Imagine large portions of the interior of this bowl are mirrors to reflect the sun’s light back to it, causing a huge jet to stream towards the hole, and in fact through it.  Imagine that the star moves; slowly, to be sure and dragging the bowl by gravity, but it does move, and never stops.
That’s the artifact that intrepid (aren’t they always?) colonists in The Bowl of Heaven stumble upon in their comparatively fast ramship.  How they meet and interact with the very alien beings occupying this artifact is the other half of the amazing idea of this book, although having conceived the thing in the first place is the astonishing bit, I guess.
The aliens are mentally and physically very different from humans and I will in my usual way refuse to tell you more, except that I do not spoil a garden by running through it.  Read the book.  There may be an audiobook of The Bowl of Heaven by now.