Tomorrow, June 21st marks the longest day of the year in the Northern Hemisphere and the official start to summer.  To celebrate the start of the season, the United States National Parks Service has granted FREE ADMISSION all day to every park and protected area in the country.

While many of America's almost 400 National Park units are free all year round, Yosemite, Grand Canyon, Yellowstone and 144 other National Parks are completely free tomorrow.

While this is a great opportunity to explore our parks, the deal can mean crowded parking lots and long lines to get in, so make sure you arrive early.

You could be spending your day here,

The

The Grand Canyon. (Joshua Lott / Reuters)

Or here,

Old

Old Faithful Geyser at Yellowstone. (Larry Downing / Reuters)

Or here,

Crater

Crater Lake National Park, Oregon. (Staff Photographer / Reuters(

Or here,

Hawaii

Hawaii Volcanoes National Park (Flickr/ Bill Tracey)

Or one of the hundreds of other parks around the country!

So, pick a hiking trail, pack a picnic and take advantage of the beauty of nature.

There are also two other dates for free entry into the parks this year: September 24 (Public Lands Day) and November 11-13 (Veterans Day weekend).  Mark your calendars.

    To find a National Park in your area, visit http://www.nps.gov/findapark/index.htm