Statue of Liberty audio guide,
five stops, free.

Look out past the railings, across the water, and find the small green figure on the low island. From here she is side-on to you. The statue faces southeast, lined up with the old fort she stands in and with the way ships came in from the open sea. Manhattan gets her profile. The harbour mouth gets her face.

Frédéric-Auguste Bartholdi chose the spot himself, on a trip across the Atlantic in 1871, when the island was still called Bedloe's Island. It was small, but every ship entering New York Harbor had to pass it, and he called it the gateway to America. It was federal land, too, which he called land common to all the states.

The round sandstone walls beside you are Castle Clinton. It began as the Southwest Battery, one of a ring of harbour forts built or refitted around 1808 to defend New York, and took the name Castle Clinton in 1817, and the star-shaped fort under the statue, Fort Wood, came out of the same programme. So you are standing by one old fort, waiting to visit a statue that stands inside another.

She arrived in pieces. On the seventeenth of June 1885 the French navy ship Isère sailed in with the statue taken apart in its hold, to a naval parade, and then she spent a year in storage, because the Americans had not finished the pedestal.

Dedication day was the twenty-eighth of October 1886, and the weather was dreadful. New York held its first ticker-tape parade, from Madison Square down to the Battery, where you are now. Over a million people turned out. On the water about 300 vessels paraded past the statue in fog and rain, with less than a quarter of a mile of visibility. The New York State Woman Suffrage Association could not get tickets to the ceremony, as unaccompanied women, so they chartered a boat and watched a colossal woman called Liberty unveiled from the water.

In 1886 she was the tallest structure in New York City: 305 feet and 1 inch from the ground to the tip of the flame, about 93 metres. Her official name is Liberty Enlightening the World, and enlightenment was the idea. It is not how she was read. Between 1886 and 1924 almost 14 million immigrants came into the United States through New York, and to them the raised torch did not mean enlightenment. It meant welcome.

When the ferry pulls out, watch the red roofs to the right of her island. That is Ellis Island, where about 12 million people passed through the halls between 1892 and 1954.

Keep walking round the promenade to the south side of the island until she is looking straight over your head, out towards the harbour mouth. This is the face everyone knows, and at this size it is enormous: the nose is 1.37 metres long, each eye 76 centimetres wide, the mouth 91 centimetres. From chin to the top of the head is 5.26 metres.

You will hear that Bartholdi gave her his mother's face. The curator of the Bartholdi Museum says there is no basis for that. What there is, is an earlier woman with a lamp. Years before this commission, Bartholdi had pitched a colossal lighthouse for the Suez Canal: a robed woman holding a light aloft, to be called Egypt Carrying the Light to Asia. The khedive turned it down. It is hard not to see her standing here.

Read the crown next. Seven rays, and under them a row of 25 windows, which is where crown visitors look out. The National Park Service describes the rays as light, like a halo. You will often be told they stand for the seven seas and the seven continents, and that is the reading most people carry home.

In her left arm is the tablet, 7.19 metres long, and you can read it from here: JULY IV MDCCLXXVI. The fourth of July, 1776, the date of the Declaration of Independence.

Now look down to her feet. Her right foot is raised, heel lifted, mid-stride: she is carrying the torch forward, not standing guard. And at her feet, out of sight from anywhere you can stand, lie broken shackles and chains. Bartholdi thought about putting a broken chain in her hand, and decided that would be too divisive so soon after the Civil War. So it went on the ground, under the robe, where almost nobody sees it.

That chain is the reason she exists. The man who first proposed a gift from France, in 1865, was Édouard de Laboulaye, an abolitionist and president of the French Anti-Slavery Society. He wanted to honour the Union's victory and the end of slavery. But liberty was a dangerous word in nineteenth-century France. It suggested revolution. So Laboulaye and Bartholdi agreed their figure would not lead an uprising. She would light the way, peacefully and lawfully. Hence the name: Liberty Enlightening the World.

The promise under the robe was not yet true for everyone who sailed past. For African Americans in 1886 the broken shackle described a freedom that had not arrived, and W.E.B. Du Bois wrote that, sailing past her on his way home from Europe, he could not feel the hope he imagined immigrants felt.

On the day she was unveiled, the twenty-eighth of October 1886, her face was covered by a French tricolour, due to drop at the end of a speech. Bartholdi mistook a pause for the ending and let it fall early. The guns went off and the crowd cheered. Asked what he thought of the finished statue, he told a reporter: my dream has been realized. I can only say that I am enchanted.

You are at the top of Hunt's pedestal, and the statue begins directly above your head. Look up. This is the view that explains everything you saw from the lawn.

That brown, folded surface is the inside of the copper skin, the back of the robe you walked around. Crossing it are two kinds of metal. The heavy girders are Gustave Eiffel's framework: a central pylon, 28 metres tall, with a truss of lighter, asymmetrical girders branching off it to follow the shape of the body. The thin flat bars, bolted to the copper and bent to follow each fold, are what tie the skin to that frame, and they are springs. Eiffel did not want a rigid statue. He built one that gives a little in the wind.

It was one of the earliest examples of what architects now call curtain wall construction, where the outer surface carries no load and simply hangs from a frame inside. Eiffel finished this in Paris in late 1883. A few years later he began his tower.

Not all of it is as he left it. He tried to stop the copper and the iron corroding each other with a layer of asbestos soaked in shellac, and by the 1980s it was clear that had not worked. The great restoration replaced the rusting iron bars with stainless steel. Inside the skin the restorers found a century of paint, took it off with liquid nitrogen, and then blasted away two layers of coal tar with baking soda, which does not damage copper. Where the skin needed patching, the new copper came from a roof at Bell Labs, because its patina already matched.

Above you the stairs keep going. The double spiral staircase inside the statue was added in 1888, and from her feet it is 162 steps to the crown; from the ground, 377. The torch is further still, reached by a narrow forty-foot ladder inside the arm, and it has been closed to the public since 1916.

Now go out onto the balcony. The pedestal is roughly half the height of the whole monument, and from up here the harbour opens all the way round, the water every one of those ships came in on. In October 2012 Hurricane Sandy put three quarters of the island below you under water, and it stayed closed until the fourth of July 2013.