网站：http://www.nps.gov

每年都有免费开放时间（FEE FREE DAYS），可以到网站上查询。

FEE FREE DAYS IN 2012

There will be no entrance fee at National Parks that normally charge on these special dates. Mark your calendar.

January 14-16
Martin Luther King Jr. weekend
April 21-29
National Park Week
June 9
Get Outdoors Day
September 29
National Public Lands Day
November 10-12
Veterans Day weekend