This is a great visit for those who are history buffs. Not only is it educational, but quite peaceful. However, I suggest that you eat before arriving since there is no restaurant on the grounds and limited snacks are sold in the gift shop. Dress with cool clothing in the summer and warm clothes during the cooler months, since you spend the greater part of the time walking outdoors.
Speaking of walking, wear comfortable shoes because the greater part of the grounds is gravel.
If you want to see everything onsite including a video that is shown every half hour, plan to spend at least 3 hours there.