The High Speed Rail is the most persuasive argument that Taiwan is smaller than it looks on a hungover Sunday. Taipei to Taichung is a short chapter. Taipei to Tainan is a longer one, and still shorter than the story people tell about “going south.”
Book on the HSR app. Non-reserved cars exist for a reason; they are also how you stand for an hour on a Friday night. If you live here, keep a default pair of trains in your head the way you keep a grocery list: the 18:06 down, the 21:36 back. Dinner in a city that is not yours becomes ordinary.
This is not travel writing. It is infrastructure. Use it.