Andromeda, a spiral galaxy, is only 12.5 times as far away as it is wide (2.5MM to 200,000 light-years), so it shows up relatively well in our sky. It's on a collision course with the Milky way--ETA is about 3.75 billion years--which makes it one of the few elements of the universe that isn't rushing away from us. Andromeda is just barely visible to the naked eye in good conditions. Human beings have been recording their observations of it since the 10th century, but only in the 19th century did its spectral lines suggest that it was not a gaseous nebula but had some kind of stellar nature. Believing it to be a relatively close object, astronomer first guessed that it was some kind of nova. In 1925 Edwin Hubble demonstrated that it was a separate galaxy similar to our own.
Even the old-fashioned pictures are pretty spectacular.