More men died in the Battle of Gettysburg than any other battle fought on American soil before or since. The 3,965 acres of the Gettysburg Battlefield is managed by the National Park Foundation.
Over and over again people recommended autumn for thinner crowds, cooler temps, and a more peaceful experience. The tress in Pennsylvanian are stunning in the fall.
When not to go - July. From everyone I have spoken to this is the most heavily visited month of the year.
However, the Battle of Gettysburg took place July 1, 2 & 3, 1863. If being there on those dates of remembrance is important to you, there is an annual reenactment of the battle. Here is information to purchase tickets to that event. http://www.gettysburgreenactment...
While all the visitors flock to Niagara Falls, head away from that attraction to find something wildly fascinating and take it in without a tourist in sight.
Summer and Fall, dawn to dusk. We found that if you go early in the day, you'll likely be the only people on the trail or near the gorge for a few hours, which offers an unspoiled view of the fierce water.