If you love the great outdoors, the second of the National Park Service‘s four dates throughout the year when you can visit any of the hundreds of parks it maintains free of charge is upon us.

On Saturday, April 21, you can visit any national park absolutely free!

RELATED: National parks lifetime passes for seniors are about to get a lot more expensive

Enjoy free outdoor adventure at our nation’s parks

The National Park Service (NPS) announced that it will waive admission fees to its parks on the following four days this year.

• January 15 – Martin Luther King, Jr. Day
• April 21 – The start of National Parks Week
• September 22 – Public Lands Day
• November 11 – Veterans Day

The entrance fee normally charged at most parks ranges from $25 to $30.

Yet the most visited park in the system — Great Smoky Mountains National Park — does not charge for entry. Under an agreement that transferred the land to NPS in the ’30s, the iconic park must remain open to anyone free of charge in perpetuity.

All told, NPS maintains 417 parks across the country. Only 118 of them charge admission.

The federal agency, which is facing a $12 billion budget shortfall, has floated the idea of jacking up the entrance fee at 17 of its most popular parks during the peak travel season. The proposed price hike could be as high as $70 and may take effect as soon as May 2018.

The slow creep toward higher prices last reared its ugly head on August 28, 2017, when the cost of a lifetime NPS pass for senior citizens skyrocketed overnight from $10 to $80.

So, if you’re into nature and can get free admission in 2018 on select days, you should consider grabbing it!