North Cascades National Park has only one highway (State Route 20) that bisects it. To the north and south are the two main units of the park, and they are wilder than most any wilderness in the Lower 48 States. Maintained trails are few compared to the immensity of the park, which means that any backpacking trip into the crown jewels of the park requires several days at a minimum. A week or two would be much better.
However, for the roadside traveler, Rt. 20, in view of Liberty Bell Mountain near the summit of the Cascades, is hard to beat. Treacherous in winter, with a little precaution you can easily travel from the cold wet northern rain forest of the west side, across the high country, and down to the dry rain shadow of the east slope.