The Christmas tree is down, the kids are back at school and the deep winter is upon us. It’s still a couple months until warming temperatures bring us dots of purple and white crocuses peeking through the ground, signaling the beginning of spring.

Between now and then, however, there are long holiday weekends that present the perfect opportunity to do some traveling. An economical, convenient, and interesting trip would be to visit one of Pennsylvania's national, and natural, treasures.

In 2016, the United States celebrated the 100th anniversary of the National Park Service, created by President Woodrow Wilson. While Yellowstone was the first established national park, Pennsylvania is home to four national parks.

Pick a park, pack the kids, and plan an outdoor adventure that stretches both your muscles and your mind: hike part of the Appalachian Trail, tour historic structures from Pennsylvania’s colonial past, or ring the bell that started the American Revolution.

Each park provides its own sense of adventure, slice of American history, and, undoubtedly, family memories to cherish.

Valley Forge National Historical Park

Valley Forge National Historical Park was the Revolutionary War encampment for Gen. George Washington's army from December 1777 to June 1778, where they would train — tired, cold, and ill-equipped.

The harsh winter of steady snow, scarce food and warmth, and rampant disease are vividly depicted. After visiting here, you will be glad you live in 2017 and not 1777; but you will also have a profound appreciation for the conditions our forefathers fought under to gain independence from Britain.

Walk the camp and tour the huts, commander’s quarters and graveyard to fully capture the transformation that occurred here. Trails connect the key monuments and historic structures, including the early 20th-century National Memorial Arch and the Muhlenberg Brigade’s recreated log-cabin barracks.

Independence National Historical Park

Hailed for centuries as the birthplace of American democracy, Independence Park houses a bell that chimed on July 8, 1776, to invite colonial Philadelphians to the first public reading of the Declaration of Independence. Visit this national park and walk in the steps of those first patriots.

In the heart of Philadelphia, Independence National Historical Park sits as a beacon to the spirit of liberty that ignited the American journey almost 250 years ago. It includes the Liberty Bell; Independence Hall, where both the Declaration of Independence and the U.S. Constitution were signed; and the state-of-the art Benjamin Franklin Museum, where the entire family can explore Franklin's life and character through computer animations, interactive displays, and artifacts.

An added benefit is that Philadelphia was named last year as the first UNESCO city in the U.S.

Gettysburg National Park

The Battle of Gettysburg was a turning point in the Civil War, when Union troops defeated Confederate troops and defeated Gen. Robert E. Lee's troops stopping their invasion of the North.

Gettysburg suffered the most losses of any Civil War battle, thus providing the inspiration for President Abraham Lincoln's immortal Gettysburg Address. See the podium from which this speech was delivered and walk among the graves of those who bravely preserved the union.

Don’t miss the renowned Gettysburg Cyclorama, which provides a panoramic view of Gettysburg’s final surge — Pickett's Charge — assembled seamlessly in hundreds of hand-painted panels. President Dwight Eisenhower’s retirement home is also located in the park and open to the public.

Delaware Water Gap National Park

Established to preserve the natural, culture, and scenic resources of the Delaware River Valley, the park includes significant Native American archaeological sites and early structures from Dutch colonial settlements.

Over 27 miles of hiking trails run along streams where waterfalls abound (Dingmans and Raymondskill Falls are the most popular), and give spectacular views of the Delaware Water Gap and neighboring mountaintops (Kittatinny Ridge). The park offers a multitude of seasonal outdoor recreational activities along its 100 miles of scenic roadways.