For the first time since September 11 2001, New Yorkers are walking freely around the giant reflecting pools at Ground Zero in lower Manhattan.

The fencing has been removed as has the entrance fee and the need for an appointment to gaze at where the towers once stood.
 
A plaza area is now open to anyone wishing to pay their respects or have a quiet time at the scene of America's biggest tragedy.
 
To one side of the plaza is the entrance to the new National September 11th Memorial Museum, housed in a building that slopes gently in the direction of where the north tower once stood. For this you will still need to find $24.
 
Along with other key news organizations, Al Jazeera was granted access to the complex a day before President Barack Obama led a moving and well produced official dedication ceremony attended by the nation's leaders. In his speech the US president said: "Today at this memorial we come together, we stand in the footprints of two mighty towers, graced by the rush of eternal waters, we look into the faces of nearly 3,000 innocent souls men, women and children of every race, every creed, every corner of the world".
 
Inside the memorial and museum
 
This underground memorial and museum is cavernous - not at all claustrophobic.
 
A gently sloping path takes you down seven stories under the reflecting pools to bedrock where it feels more like an archeological dig than a museum.  It's here that the square box joints that once lined all four sides of both towers, helping to prop them up, can still be seen.
 
Also down here is the vault that contains thousands of unidentified body parts.  Effectively, a branch of the city's medical examiners office. The public will never be allowed in - all that can be seen from the outside is a quote from the author Virgil: "No day shall erase you from the memory of time". 
 
Some family members are unhappy that the remains are here but the museum promises to take great care of them in the hope that one day advances in science will allow the identity of all victims to be known.
 
Artifacts, audio and video
 
Remembering what happened 13 years ago, the people it happened to and why it happened to them are the chief aims of the memorial and museum.
 
Powerful exhibits include part of the TV aerial from the north tower - the motor from one of the elevators - and a fire truck from the FDNY's ladder company 3 in Manhattan's East Village bearing an inscription written anonymously, "Jeff we will not forget you"  The cab of the fire engine was sheared off when the north tower fell.  It's hard not to wonder what the final thoughts of all 11 responding crew members were.
 
Also most impressive is the giant slurry wall that once held back the nearby Hudson River.  Its size is astounding.  It was lovingly removed and reassembled in what's now known as Foundation Hall, where the dedication ceremony took place.
 
The story of 9/11
 
The centerpiece of the memorial is the main museum. It's where you'll find most of the artifacts which, unlike the big towers, are mostly small and include things such as teddy bears, business cards that fluttered down from on high, pictures and personal items such as watches and shoes. 
 
Florence Jones was one of a small number of people who escaped from the south tower on 9/11. She spoke at the dedication ceremony about why she donated the shoes she had on at the time.
 
"When I heard that the museum was looking for artifacts I thought about my shoes.  I had put them in a plastic container and when I took them out they still had the smell on them from that awful day and I knew I would never wear them again"
 
One of the exhibits deals with the rise of al-Qaeda.  It's narrated by the famous US news reader Brian Williams.  While factually correct, many Muslims worry it paints 1.5bn people who follow Islam as terrorists.  The museum denies it.

Alice Greenwald, the museum director, told al Jazeera the Muslim experience of 9/11 is well documented throughout the museum, beyond the al-Qaeda exhibit.

"We over and over and over again make it clear that this is not mainstream Islam we're talking about, this is a radicalized group of people with a murderous agenda who are being treated as criminals in this museum"

Overwhelming experience
 
The memorial and museum make for an overwhelming experience. Time and again you're looking at steel twisted by the impact of aircraft and heat - as if it were only yesterday.
 
Everyone will have a different view of course. Some will boycott it as too ghoulish. Others will attest that it's an homage to the terrorists and should be shuttered.  
 
Americans, however, have a knack for putting on memorials and museums and most people - I think - will say it's an unfortunate but necessary learning experience.
 
Whether you think 9/11 was carried out by pure evil human beings or evil human beings reacting to discredited US foreign policy - I predict that you'll come away with at least two impressions.
 
1. How very big the World Trade Center site really was.
 
2. How sad this has all been for everyone involved - everyone.