JR Yamanote Line
Originated in 1885, the JR Yamanote Line is one of Tokyo’s busiest and most important commuter rail lines, connecting most of Tokyo’s major stations and urban center.
Running as a loop line around central Tokyo, a complete loop takes about an hour, with each of its 29 stations having a distinctive arrival and departure tones.
Below is a YouTube video of the entire Yamanote loop sped up 10x – cool!
Of course, I have ridden the Yamanote Line many times while living in Tokyo, but have not yet visited all stations yet so this is a good reason to go back to Tokyo.