Over the past few years, it has become a tradition for the National Park Service to waive entry fees into the national parks several times a year. Those fee free days have become extremely popular with frugal travelers, who take advantage of the lack of an entry fee to enjoy some of the best natural wonders that America has to offer.

Earlier this month the Park Service announced their fee free days for 2011, giving us all a number of great opportunities to enjoy "America's Best Idea" on the cheap. Several of those days, Martin Luther King Jr.'s Birthday weekend, have already slipped by, but here are the remaining fee free days for the year.

• April 16-24 (National Park Week)

• June 21 (First day of summer)

• September 24 (Public Lands Day)

• November 11-13 (Veterans Day weekend)

In all, there are 14 days remaining in 2011 during which you can gain entry into more than 100 national parks for free. To see a complete list of which parks will be waiving their entry fee on those days click here.

Knowing the available dates well in advance allows us to plan ahead and select which parks we would most like to visit during the fee free days. For example, in April many of the parks are still on the cool side, but it is an excellent time to visit Big Bend in Texas, before it becomes too hot. The first day of summer seems the perfect excuse to drop into Denali, located in Alaska, while September is great for visiting Yellowstone. As for November, how about stopping by the Everglades for one last tropical escape before the winter snows start to fly across much of the country.

Whether they're free or not, the national parks are fantastic destinations all year round. But it never hurts to get something for free!

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