This weekend, all 397 national parks, including Yellowstone and Grand Teton, are letting visitors in for free.

The free admission is in honor of the coming Martin Luther King Jr. holiday weekend.

Normally, admission for a private, noncommercial vehicle to Grand Teton and Yellowstone is $25 dollars for seven days.

Common park activities this time of year include cross country skiing, snow shoeing, watching wildlife and photography.