A very sobering but interesting experience.
It is situated deep underground with 2 main rooms under the memorial pools. The first is dedicated to all the people who lost their lives - with walls of their photographs and a place where individual names and details are read out on a continous loop. There are a few personal artifacts there, including a wallet from a British man that contained his Sainsbury reward card!
The second room has a timeline of how the attacks unfolded from the first breaking newscast and includes details of the phone calls made by people in the hijacked aircraft. There are also items recovered from the area such as burnt sheets of paper, melted telephones and seat belts from the plane. There is an section on the terrorists and the political situation as well. Not surprisingly, no photos are allowed to be taken in these areas.
However, you could take photos in the surrounding areas - this is the front of a fire engine crushed when the tower came down.
This is the last remaining column that was removed from the site and is covered in badges and details of the Police and Fire agencies involved in the clearance of the rubble.
There are other interesting items too, such as this old motorcycle that was bought by a fireman but who never lived to restore it. Instead it was restored by his colleagues in memory of him and his other officers who died from that station.
A piece of the aerial that was on the top of the towers. We spent over 2 hours there and would recommend it to anyone who gets a chance to visit.