There are 3-4 of these free entry days during the year.  The next one is April 21.  I've got a bucket list of national parks I would love to visit!  
https://www.nps.gov/index.htm
https://www.nps.gov/subjects/npscele...-park-week.htm
					https://www.nps.gov/index.htm
https://www.nps.gov/subjects/npscele...-park-week.htm
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