Wulai, a very interesting and scenic place. If I got more time I'll come back and edit this post to put in more details.
There's this 80m famous Wulai fall. There's this Old Street selling many local Atayala tribe's delicacies. From Wulai fall I walked 1.5 hour (I walked very briskly) to reach Nei Dong Natural Park (it's a long long walk, but highly recommended - otherwise you can pay TWD200 from the cable car station and take a taxi where it'll take about 15min to reach via road), a even more scenic place where there are numerous falls and a famous 3 layers waterfalls. It is reputed to be the place with the most concentrated negative-ions in Taiwan. Azure water with breaking rapids throughout the Nan Xi river where all the falls stream into.
And there's this free hotspring. Truly fantastic place for a day visit.