Free Entrance Days in the National Parks
America’s Best Idea – the national parks – gets even better with several fee-free days at more than 100 national parks that usually charge entrance fees.

Mark your calendar for these fee-free days in 2011:
* January 15-17
(Martin Luther King, Jr. Birthday weekend)
* April 16-24
(National Park Week)
* June 21
(First day of summer)
* September 24
(Public Lands Day)
* November 11-13
(Veterans Day weekend)

More details at this link.