Like most Asian countries, Taiwan has plenty of night markets. Some of them are very commercialized, so expect big crowd. If you don't like Crowded areas, maybe go for the less commercialized ones.
We went to Shilin, Raohe, Liaoning and Keelung City night markets.
Food was the main attractions. Also had toys and fashion merchandise.
Shilin and Raohe were very crowded. Liaoning was pretty much a small neighbourhood night market, much smaller and much less crowded. Keelung was just right for me.