The next two least visited national parks, Isle Royale and Kobuk Valley, don't get any easier visitation-wise.
Kobuk Valley NP is in, you guessed it, Alaska. Located next to it's neighbor Gates of the Arctic, this park has no roads. Flying in by charter plane is the main way hikers access it's lands. The size of Delaware, Kobuk Valley is famous for it's great sand dunes and Caribou herds. These sand dunes were deposited after the last major glaciers retreated during the last ice age. Located 25 miles above the Artic Circle, Dogsledding is also a popular way to tour the park.