I went there once, by bus from Xinnanmen tourist bus station. I think the bus should take something like 6-9 hours. There are two different routes. Both take roughly the same amount of time. One of them goes over mountains. That one had very nice scenery.
It’s really easy to get around there. There’s shuttle buses in the park that take you between the scenic spots. You can also go for a hike around the area. Walking around the whole area takes a day I think. Or maybe two.