Whanganui National Park's main attraction is the Whanganui River, which curls its way 329km (204mi) from its source on the flanks of Mt Tongariro to the Tasman Sea at Wanganui. The fact that the river is the longest navigable river in the country has been shaping its destiny for centuries.

Historically a major transport link between the sea and the interior of the North Island, first for the Maori and then for the Pakeha, the route was eventually superseded by rail and road. Many recreational canoe, kayak and jetboat enthusiasts now use it to reach the isolated interior of Whanganui National Park.

The native bush is thick podocarp-broadleaved forest, with many types of trees and ferns. There are also traces of former Maori settlements along the river in various places. Old pa (fortified village) and kainga (village) sites crop up, as well as the unusual Hauhau niu poles of war and peace at Maraekowhai, at the confluence of the Whanganui and Ohura Rivers.

The Whanganui River Rd, running along the river most of the way from Wanganui to Pipiriki, is a scenic and historic route worth making the detour to see.