Taiwan Museum Day is on every May-18 (518).
Most national/private museums/galleries will join this big event.
They offer a good discount even free entry to the public.
We chose the Shihsanhang Museum of Archeology as our visit stop.
It is located in Bali, Taipei County where is surrounded with the ocean and mountains.
From here, you can discover the prehistoric remains and the way that archaeologists go about excavating dig sites.