One can visit the web site "Rendering Larry Niven's Ringworld" at http://www.rahul.net/rootbear/graphics/ringworld/ for a visual
illustration of looking down on
Ringworld. It has some amazing
visual perspectives that give you a very good sense of what it would be like to approach a
structure of this magnitude. In particular, it is quite instructive to view the ring against the background of
space and
stars. One is also struck by how hard it is to see the ring from
interplanetary distances.
Incidentally, the mass of our sun is 1.989 x 10^30 kg which is only about 1,000 times the mass of the Ringworld.