The valley known for purple butterfly-watching is not one geographical location, but a number of sites around Maolin National Scenic Area. The best time to watch the butterflies is between 9am and 11am, November to March. On cooler or rainy days the butterflies remain motionless, hanging from the trees like garlands.
Some sites will be signed as you drive along the main road, but enquire at the visitor information centre for good butterfly-watching locations. The centre is located where County Rd 132 meets Hwy 27, before the entrance of the scenic area. It's possible to arrange a tour with De En Gorge Guesthouse.