The most interesting timezone I ever encountered is Europe/Moscow on and around January 1, 1900. If you decide to use that date as a zero date in your code (for example, to handle the transition from two digits per year), you will be in a lot of pain: the offset was +02:30:17. Yes, with 17 seconds! Demo: https://go.dev/play/p/lq36Plr1sIL