Rocky Mountain National Park, and national parks across the country, will offer free admission on ten days in 2017.
There are more than 400 parks across the country. Colorado has four national parks -- Rocky Mountain National Park, Mesa Verde National Park, Sand Dunes National Park & Preserve and Black Canyon of the Gunnison National Park.
April 15-16, 22-23, the weekends of National Park Week
August 25, National Park Service Birthday
September 30, National Public Lands Day
Nov. 11-12: Veterans Day weekend
On free admission days, entrance fees, commercial tour fees, and transportation entrance fees are waived. However, other fees such as reservation, camping, tours, concession and fees collected by third parties are not waived.
In the Denver area, several museums and the Denver Zoo also offer free admission days. See the list here.