There are 423 units in the National Park System, but a surprising number of people focus on about two dozen parks. Last year, when roughly 300 million visited the park system, just 25 units – the Yellowstones, Grand Canyon's, Zions, Cape Cods, Blue Ridge Parkways – got 50 percent of the traffic. There are so many overlooked units in the National Park System worthy of a visit. They might not be your final destination, but they're certainly worth becoming a destination on your traveling itinerary. For example, let's walk the tallgrass prairie at Tallgrass Prairie National Preserve.