I spent 2 days there.
1 day - An Ping area. Purchase a day trip ticket which entitles you to unlimited bus ride in Tainan. Route 88/99 brings you to most attractions in An Ping eg. An Ping Gu Bao (some fort thingy), An Ping Old street, Tree House, Sio House and more..
the 2nd day I went to Shi Gu Wen Hua Chun (10 Drums Village?), imo it's quite boring here, you can try google and see if it's your cup of tea. After Shi Gu, I took a walk to Bao An Station where you can buy a ticket from Bao An Station to Yong Kang Station. Apparently the ticket is quite popular as the ticket shows "Yong Bao An Kang" when read anti-clockwise.