Suggestions Wanted: Out of Taipei, No Car, Rainy Weekend

So, lovely Taiwan expat community - I urgently seek your suggestions. By "urgently" I mean "like, tomorrow". 

My in-laws are in town this week, and we have avoided making weekend plans until now because of the unpredictable weather. We're happy we did, because it looks like our original hope of going to the east coast is going to be so marred by rain that it won't be worth it. I want to get out of Taipei - haven't left since we got back from Turkey - but the in-laws would be fine staying in town as this trip is fairly short and they're more interested in seeing us than in some spectacular sightseeing trip.


We're now trying to figure out what to do. Some ideas, with questions:

• two day trips, one to Daxi/Fuxing and the other to Jiufen/Jinguashi (no question here, except, anywhere really worth eating in Jiufen/Jinguashi? I have trouble finding good food out that way. My mother in law does not eat seafood or fish. AT ALL. That's why Donggang is out). They've never been to an old street and "having coffee and looking at the reservoir sounds lovely".
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• HSR to Kaohsiung and charter a taxi to go out to Maolin Scenic Area and up to Wutai. Feasible? Can we plan this on short notice? How're the butterflies doing? Once there is it even possible to arrange for transport help from whatever hotel we'd stay at (can take care of that tomorrow), or would we be looking at one very long day trip from Kaohsiung or Pingdong? Renting a car is not an option: none of us have international driver's licenses and even if we did, none of us feel confident on Taiwanese roads. No scooters - neither of us has driven one and with our parents on the back is not the time to learn! 

• Sun Moon Lake. Blech. I don't really want to go there, but this weekend is a working weekend for much of Taiwan so maybe it wouldn't be so bad? Then again hordes of Chinese tourists not diluted by domestic visitors almost sounds worse...

• Taroko is out because heavy rain is predicted for much of the east coast this weekend

• They've already been to Tainan, so we don't see the point in going back with them or going to Lugang. They went to Yehliu today. They've been to Taiwan once before and have seen all the must-sees in Taipei.

• Beipu? I enjoyed it at least, years ago. But we couldn't do Shitoushan - my mother-in-law is not up for hiking. This is also why we ditched Alishan and Little Liuqiu as ideas.

• Other suggestions...?