Messier 33, also called the Triangulum Galaxy, is a member of our local Group, and is "only" 2.3 million light years away. Though it looks impressive, it is only a half the diameter of our own Milky Way Galaxy and a third of the size of M32, the Andromeda Galaxy (which is also visible in the same part of the sky). 

At dark sites it's a naked eye object so it's probably not correct to say it was discovered by Charles Messier, but it was he who catalogued it in 1764.

This galaxy is notoriously difficult to present well in an image as its arms are not very bright. In this version, I have added the red light of hydrogen alpha to mark the many glowing gas clouds in the galaxy.