Celebrated every year on November 17.
Take a Hike Day was probably created by the American Hiking Society. Though they seem to have their focus on other special days now.
People all over the world celebrate this holiday independently by taking a brisk walk to somewhere they usually would think of as too far to walk and have a backpack with essentials along.
Bottles of water are of course essential, a first aid kit to treat blisters and of course you should always bring your towel.