Question: When did the Stonehenge visitors' center open to the public?
About the article "Stonehenge", section "Setting and access".

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The A344 was an A road in the English county of Wiltshire.
It ran from its junction with the A303 road at Stonehenge north west to its junction with the A360 road, away.A344 was once part of a longer route, stretching from Andover in the East to Warminster in the West.
The section from Andover to Amesbury was redesignated as the A303, when the new route to the south west was created to bypass the A30 to the south.
The western section, from Shrewton to Warminster has been re-classified as the B390.
The remaining section passed close to Stonehenge.
In July 2012 work began on a £27m project which involved the closure and grassing over of A344 between Stonehenge Bottom and the monument, with the pedestrian underpass beneath the road being filled in.
This section of road was eventually closed in June 2013.
The new Stonehenge visitors' centre at Airman's Corner (or Airman's Cross) opened in December 2013.
Vehicle traffic on the remaining section of the A344 is now restricted to mostly shuttle buses providing transport from the visitors' centre to the monument.
The shuttle bus service found it could not cope with demand during the fourth weekend after opening.
Long queues developed and many visitors choose to walk to the Stones rather than wait for the buses.
Therefore, the A344 is no longer a road open to public vehicular access.
As the closure of the section between Airman's Cross and Byway 12 was by means of a traffic regulation order prohibiting motor vehicles, this section still remains a public highway.
A memorial to Major Alexander William Hewetson, of the 66th Battery Royal Field Artillery, stands besides the old A344 at Fargo Wood, west of Stonehenge.
Major Hewetson was killed in a flying accident on July 17th 1913. 
The festival attendees were viewed as "hippies" by the wider British public (some were, in fact, self-described hippies).
This, along with the open drug use and sale, contributed to the increase in restrictions on access to Stonehenge, and fences were erected around the stones in 1977.
The same year, police resurrected a moribund law against driving over grassland in order to levy fines against festival goers in motorised transport.
However as late as 1984 the police-festival relations were relaxed: just a nominal presence (two police constables) in the car park.
On solstice morning people sat on the stones and offered their spliffs to the police below, who politely declined.
The right of the Stonehenge festival to occur had been historically contested, and that trend was dramatically resumed in 1985 when English courts banned the Free Festival from being held at Stonehenge.
The ruling came so late that some Free Festivallers did not know about it, and several hundred attempted to show up in defiance of the ruling. 
The Stonehenge Landscape is a property of The National Trust, located on Salisbury Plain in Wiltshire, England.
The estate (formerly known as Stonehenge Historic Landscape and before that as Stonehenge Down) covers surrounding the neolithic monument of Stonehenge which is administered by English Heritage.
Much of the land is designated open access by the Trust, including the fields immediately around Stonehenge and other fields that become available as part of the chalk grassland reversion project (see below).
Much of the land was acquired in 1927 after a public appeal was launched to prevent further development on the fields around the monument.
The successfully purchased land was given to the Trust for the benefit of the nation.
Shortly afterwards such structures as cottages and an old World War I aerodrome were removed from the immediate vicinity of the stones.
There are two different memorials to fatal flying accidents in the area.
Eustace Loraine and Staff Sergeant Wilson were killed in 1912 near to the new Stonehenge Visitors' centre.
Major Hewetson was killed in a flying accident near Fargo Wood in July 1913.
Later the Trust acquired more land, principally after the purchase of an adjacent farm in the early 21st century.
The land owned by the Trust comprises almost one third of the Stonehenge World Heritage Site, and contains nearly 400 ancient monuments (most of them scheduled).
These monuments include the enormous earthwork known as the Stonehenge Cursus, the Avenue, Woodhenge and Durrington Walls as well as numerous burial mounds known as barrows.
The estate also includes some of the Nile Clumps, large clumps of trees on arable farmland, said to represent ship positions at the Battle of the Nile.
This is said to form a large memorial to Nelson created by a local landowner after Nelson died.
During the 1970s and 1980s the estate was the scene of the Stonehenge Free Festival.
Damage to monuments such as the Cursus barrows was one of the reasons that the festival was banned in 1985.
As part of the World Heritage Site Management Plan for Stonehenge, some 340 hectares of the land will revert to chalk grassland by 2011.
The scheme (one of the largest reversion schemes of its kind in Europe) will turn over much of the estate to permanent pasture, and allow for increased open access around the area.
At present some 112 hectares have reverted, and along with the existing grassland are used as public open access as well as animal grazing. 
The windmill is open to visitors when it is turning. 
The estate is not open to the public.