Free entry to national parks is available during National Park Week.
The pair will compete at the Mattoni Olomouc Half Marathon on June 21.
The One Fund Boston is the primary fund that benefits the more than 250 victims of last year's bombings.
More than 3,000 police officers will be on hand to keep the marathon safe.
The two-time Olympian says other partnership deals are in the works.
The 59-year-old will run his race in memory of a child killed in last year’s terrorist attack.
Flanagan wants to win the Boston Marathon more than any other race.
Webb, 31, retired from track and field this past winter.
Kastor runs 1:11:38 to set new U.S. 40-and-older mark.
Mo Farah placed eighth in his full marathon debut but vowed to run another one.