Catch some of the country's first flowers in Oklahoma's Ouachita Mountains. BY ERICA ZAZO

To kick off National Park Week, National Park Service sites across the U.S. will offer free entry on April 21. For many of the 118 NPS sites that aren’t already free, Saturday could be a busy day. Places like the Grand Canyon and Yellowstone, which already get millions of visitors a year, will fill up when the fees drop. To help you skip those crowds, we scoped out 9 great hikes in the least-visited NPS sites where you usually have to pay to play. Get outdoors for a day trip this Saturday, avoid the crowds, and steal a great deal.

The Midwest's best multiday trips, as selected by BACKPACKER Local scout Erica Zazo.

With a bit of luck, you can see nature’s most electric light show.

Can hikers leverage vacation rentals to turn Los Angeles's 67-mile Backbone Trail into a legitimate thru-hike? Will Cockrell investigates.

Get ready for your AT thru-hike with this gear checklist from expert thru-hiker Liz "Snorkel" Thomas.

In these backcountry paradises, rain is part of the adventure.

Headed out on the Pacific Crest Trail? Expert thru-hiker Liz “Snorkel” Thomas breaks down the gear you’ll need.

The best local trails, as selected by BACKPACKER Local scout Brad Stapleton.

The best local trails, as selected by BACKPACKER Local scouts Paulina Dao and Daniel Markey

The best local trails, as selected by BACKPACKER Local scouts Anastasia Allison and Jason Bickford.

The best local trails, as selected by BACKPACKER Local scout Erica Zazo.

The best Big Apple escapes, as selected by BACKPACKER Local scout Justin Bailey.

The best local trails, as selected by Denver Scout Heather Balogh Rochfort.

The best local trails, as selected by our BACKPACKER Local scout Scott Jones.

The best local trails, as selected by BACKPACKER Local scout Stan Gentry.

The best local trails, as selected by BACKPACKER Local scout Daniel Nelson.

Nikwax's head of customer service shares what he loves about Mount Rainier National Park.

From prickly pear desert to verdant gorges, this hike shows off the range of the Lone Star State.

A jaunt down a stream is a less in what water can accomplish.

Leave the crowds behind: Tackle Mt. Marcy in winter, and it will be just you, the silent mountains, and a whole lot of snow.

When Marine Sergeant Kirstie Ennis lost her leg above the knee in Afghanistan, she found healing in the outdoors. Now, she has her sights set on the world’s highest mountains.

Protecting land is only the first step. Hikers need trails, and trails don’t build themselves. Grab a Pulaski and create new paths and restore lost routes on these 10 trips.

Hit these endangered trails to vote with your feet and send a message that protection pays off.