Paris was a city I knew well before I ever visited it. As a child I would study street maps, locate buildings I'd heard of, follow convoluted metro journeys. I did the same for Moscow, New York, even London even though I lived barely fifty miles from it. I did not visit France until I was 25, and not Paris until a few years after that. But it was just as I expected.

Except, of course, for the gaps in between the places I knew so well. That is why the only way to get to know a city is to walk it. I feel that I have spent most of today walking, a day that started at about half past seven with a double espresso at a corner cafe by the Rue des Levis street market. I took the metro from Villiers to the bizarre Arts et Metiers station,which is like a Terry Gilliam interpretation of a Jules Verne submarine. I changed there and got off at Pont Neuf. The light at this point in the day was fabulous, spilling westwards from beyond the Île de la Cité, and I walked into it along the quai of the Seine to Notre Dame.

The square in front was no less busy than it had been twelve hours before, and after fantasising briefly that I was the only one who had left, I stepped inside the cathedral.

I had fond memories of Notre Dame from previous visits, but I had not expected it to be quite so busy. It was shoulder to shoulder at the west end, and the interior of the nave had been sectioned off with ropes in a vain attempt to control the crowds. At first, I took many of them to be Japanese, and could not understand why they were being so badly behaved, blocking the gangways, using flash when the signs said not to, talking when the signs said silence. This seemed most un-Japanese like. And when I got close and could hear their voices I realised that, of course, they were not Japanese at all. They were Chinese, and this was a big difference between the Paris I remembered and the Paris I was seeing now, for thirteen years ago who could have imagined that there would be mass Chinese tourism to Western Europe?

What else has changed in Paris? Among other things, the fast food adverts carry a health warning - 'for a healthy lie you should eat a balanced diet' and 'everyone should eat five portions of fruit and vegetables a day', and so on.

So I shoved my way through the nave as if I was in a dour provincial bus station, and made it into the aisles. Notre Dame is not a huge cathedral, and I decided that I still liked it a lot, despite the crowds. Lots of the visitors were using iPads to record their visits, one girl wandering around with it in front of her face, videoing what she might otherwise have observed. She was experiencing the cathedral through the iPad.

I watched her for a while and then headed down the Île to Ste-Chapelle. Here, the walls of 13th century glass are breathtaking in their intimacy. There is a rolling programme, currently in its fifth year, to restore it bit by bit. So far they've done the south  side and the east end, and comparing the restored glass to that still awaiting restoration, the result is stunning.

I pottered across to the Rive Gauche, and became distracted by second hand book shops for a while, before wandering to St-Severin. This church is like a breath of fresh air after the two giants on the Île de la Cité, a fine medieval church with double aisles, and some fabulous glass. The clerestory contains more 14th century glass than there is in the whole of  East Anglia, and the east end is filled with excellent glass of 1970 by Jean Bazaine. Best of all, the 19th Century glass all depicts biblical scenes featuring the real life faces of the donors - this works well in, for example, the 'foot of the cross' scene and the 'suffer the children' scene, but is slightly bizarre in 'the beheading of John the Baptist'.

Wandering in this area I found myself increasingly distracted by second hand book and record shops, so it was not for another hour or so that I made it to St-Sulpice. This is a huge late 17th century church as big as a cathedral - imagine St Mary Woolnoth on acid and after a really huge breakfast. And yet, I found I liked it very much indeed, not least because there were lots of people inside, but not tourists. Rather, they were lighting candles, or sitting in thought, or just walking quietly through the vast spaces. And not an iPad in sight.

I wandered on past the Jardins du Luxembourg to Rue de L'Odéon. This is a smart street of tall 18th century buildings. Most of them are high end women's fashion shops, but a couple of older book shops survive. It was in this road that Sylvia Beach set up Shakespeare & Co, and a plaque above number 12 remembers the publication of Ulysses.

 Ulysses by James Joyce

Above number 4 is a plaque remembering Thomas Paine, 'an Englishman by birth, an American by naturalisation, a Frenchman by decree' who lived here during the revolution and wrote The Rights of Man here. Paine was born in East Anglia, at Thetford in Norfolk, spending his schooldays at Diss in the same county. I remember the poet and Singer Patti Smith saying how proud she was that her ancestors came from Larling at this time, almost exactly halfway between Thomas Paine's two towns. Curiously, there is no plaque at number 16, where Ernest Hemingway lived during his years in Paris.

I was headed towards the Panthéon, but got distracted yet again by an excellent second hand cd shop specialising in classical music and with a large contemporary section. I bought Francis Bayer's instrumental and vocal works and Charlotte Hug's Neuland for solo viola, both for just 3.50 each. I walked past the Panthéon to St-Etienne du Mont, a fine looking church with a minaretesque tower, and three sets of steps, allowing each door to be reached from the sloping street. At the most southerly steps there were groups of young people taking each other's photographs. They were there for the same reason I was - these are the steps where the drunken Owen Wilson waits to get taken back to the 1920s in Woody Allen's Midnight in Paris. There was even an empty bottle of wine to prove that Wilson had been there. 

I tried the door of the church, but it was locked. I discovered the uncomfortable truth that the Internet is not always right. It was true that the church had opened at 9.30am and would close at 7.30pm, just as the Internet said. What the Internet omitted to mention, however, was that it was also closed between midday and 4pm. I would have to come back. Oddly, directly opposite the steps where Wilson waits is an English pub called the Bombardier, owned by Charles Wells. Fascinated, I peered inside at the bar, set out in the style of a London pub. Chalked above the bar were the prices. You could get a pint of Courage Directors for 5 euros.Most of the patrons appeared to be young French people.

I wandered down through the Sorbonne to Cardinal Moines metro station, and crossed back into north Paris to visit the splendid-looking 19th Century church of St-Antoine, but here discovered exactly the same thing. The church had been open, but had closed for the early afternoon. I walked on down the vast Boulevard Haussmann, and just short of the Arc de Triomphe I was at last rewarded by the church of St-Sacrament. This is on the first floor of a modern building, but contains something rather surprising, certainly not something you see every day. This is the exposed body of a Saint.

St Pierre-Julien Eymard in a casket at St-Sacrament

His name is St Pierre-Julien Eymard, and he founded the order of the Blessed Sacrament. He was made a Saint in the early 1960s. he lies here in a glass casket, like Snow White, albeit more wax than  flesh, but still worth seeing.

 I set out later in the afternoon to see some churches on their second shift, but again things did not work out as planned. I wandered down from Bourse to Notre Dame des Victoires, which the Internet said closed at 7.30pm. I arrived at 6.30pm to watch them locking up. I wandered down past Les Halles to an old favourite, St-Eustache, to find the same thing, although they had an excuse as there was a concert on that night. It took St-Nicholas aux Champs to save the day, still open and not looking ready to close yet. Like St-Severin it has a double aisle right around the apse, but the most striking thing is the sheer height of the nave, dwarfing the aisles and with a clerestory of vast flamboyance windows.

I walked as far as Arts et Metiers, caught the metro back to the Place du Concorde, walked down the Champs Élysées to the Arc de Triomphe and climbed to the top to watch the sun set behind Paris, the lights coming on, the shapes fading into darkness, and making of it a city I did not know and had never seen before.