This is a beautiful and peaceful place. There is a visitors center where you learn about the events of the day (9/11). The dark area above is an observation deck where you can see the crash site. It is lined up in the direction the plane traveled.
From there you can see a gate, again, lined up in the direction of travel and a boulder that indicates the point of the crash. The gate is only opened on 9/11 and only family members are allowed to walk through it to the boulder.
Next to the gate is a long marble wall. Next to that, the wall is composed of individual marble slabs, each carved with the name of one of the passengers and crew. Each slab is different signifying the individuality of all the victims.