TRIANGLE, Va. (AP) — President Barack Obama and the first family went hiking at Prince William Forest Park in Virginia on Sunday. Their visit comes as the National Park Service celebrates its centennial.

The president has marked the week by creating a national monument in Maine and expanding a monument off Hawaii.

READ MORE: 'Serious' Crash Slows Traffic On I-97 In Anne Arundel County

Admission to national parks and historic sites was free during the weekend.

The National Park Services describes Prince William Forest Park as a “respite of quiet and calm” amid the hustle and bustle and frequent traffic jams of northern Virginia.

READ MORE: Ravens' Humphrey Likely Out For Season After Injury Against Steelers, Reports Say

The agency says the park has 37 miles of hiking trails that meander through some 15,000 acres. It is the largest protected natural area in the Washington region.

Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

MORE NEWS: Gervonta 'Tank' Davis Keeps Perfect Record Intact With Unanimous Decision Over Isaac Cruz

Follow @CBSBaltimore on Twitter and like WJZ-TV | CBS Baltimore on Facebook