1. National Public Lands Day. National Public Lands Day (NPLD) is the nation's largest, single-day volunteer event for public lands-local, state, and federal. It's also a fee free day in all national parks, so even if you are not able to volunteer, you can still visit and enjoy the parks. Find a participating site.
2. Lantern and Candlelight Tours. Have you ever wondered what famous battlefields and buildings hold at night? Explore them at Appomattox Court House NHP September 21 & 22, Kings Mountain NMP October 6 & 7, and Ninety-Six NHS October 13. All events are fee-free.
3. It's Harvest Time! Head to Booker T Washington NM September 22,  Hopewell Furnace NHS or Martin Van Buren NHS September 17, and Homestead NM of America  October 7 to explore the food, crafts, and activities that help us welcome the autumn season! These events are free.
4. Heritage Festivals. Spend the day at Cumberland Gap NHP for the Appalachian Heritage Fest September 21-23. Or explore Quaker heritage at New Bedford Whaling NHP on September 2. These two events are free. You can also head to Prince William Forest Park for their 2012 Heritage Festival on October 13. Cost is $5 per vehicle.
5. Buffalo NR. The river is turning 40! This year marks the fortieth anniversary of the country's first national river. Spend the day with the rangers and their partners to celebrate the river on September 1. This is a free event.
6. Virginia Archaeology Month. Learn about the Civil War through archaeology at Petersburg NB October 20. This event costs $5 per vehicle entrance fee. Or head to Jamestown Glasshouse October 13 & 14 and see special demonstrations-including "You draw it, we make it" where you can see your idea for a glass piece come to life. There will also be a glass raffle and the glassblowers will get creative with their own designs. Cost is $10 per adult, children 15 and under are free.
7. Andersonville NHS. Join staff and visitors in honoring those who were Prisoners of War and those who are still Missing in Action. This is event is free.
8. Ghosts! Get in the mood for the creepiest time of year and explore the ghosts of  the past at Allegheny Portage Railroad NHS on October 13 ($2 per person) or at Arkansas Post NM on October 20 (free).
9. Cowpens NB. Enjoy a Backcountry Holiday on November 18 at the battlefield. This is a free event.
10. John F. Kennedy Birthplace NHS. Join the park in the remembrance of President John F. Kennedy.

Bonus:  Are you ready for a zombie attack? Head to Fort Washington Park September 15 or 22 and find out! Explore why the fort is the perfect place to survive the zombie apocalypse. $5 park entry fee.

Entry fees to all the parks mentioned above may apply even if an event is listed as free. Please check the park's website on NPS.gov to verify fees as they may change seasonally.