The Andromeda Galaxy (aka Messier 31) has been estimated to be somewhere around 2.5 million lightyears away from us here on Earth. Due to its relative size and proximity to the Milky Way, Andromeda can actually be observed with the naked eye in the night sky.

Also because of its blueshift we can determine that it is approaching our galaxy at around 110 kilometers per second.

That means that in around 4 to 6 billion years (or 4 to 6 gigayears, if you want to be cool), Andromeda and the Milky Way will collide (or rather merge) with each other, forming a giant elliptical galaxy often referred to as Milkdromeda✨.

Further reading

Neil deGrasse Tyson: Collision of the Milky Way and Andromeda

Wikipedia: Andromeda–Milky Way collision

The Astrophysical Journal: The M31 Velocity Vector. III.