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As we celebrate the 100th birthday of America’s national parks, it’s estimated that a record number of visitors will travel to one or more national parks this summer.

The numbers will be at all-time highs at the better known parks like Yosemite and Yellowstone.

But there are 411 national parks and monuments in the U.S., and most are less visited.

Then there are the truly hidden gems—former national parks that are still worth a visit.

These are the places where so few people go that the park service actually delisted them.

Have you ever heard of Wheeler Geologic Area? It’s in Colorado.

It’s one of America’s most unusual landscapes and you have to drive 13 miles on a dirt road to get there.

The Park Service dropped it in 1950, and it became known as a ghost park because of its low visitation.

Even Mackinac Island in Michigan is considered a ghost park—it was established in 1875 as America’s second national park and was delisted 20 years later.

For more information about visiting national parks, check out:

• Where You Can Go Stargazing at National Parks This Summer
• Peter Greenberg’s Hot Destinations for 2016: National Parks
• Where You Can Find Nature Centers in National Parks

Keep reading for more travel tips.