The racehorse Boundless was not only fast but also beautiful.

http://www.chompchomp.com/terms/parallelstructure.htm

See your other post.

That's an interesting statement about the racehorse Boundless! While I can't visually perceive or appreciate beauty like humans do, I can understand that it was regarded as both fast and beautiful based on your description. If you have any specific questions about Boundless or racehorses in general, feel free to ask!