We live in a secular age, but more people than ever before - in all religions - are going on pilgrimage. Peter Popham reports on the spiritual travel boom and identifies the main destinations

We are told that we live in godless times, yet more and more people all over the world are going on pilgrimages, as if being on the road to somewhere holy suits us better than being inside the building at the end of it.

The new pilgrims are Christians and Muslims but also Jews, Buddhists, Sikhs, Hindus and Jains. There are also swelling numbers of "don't knows": people with little commitment to any established religion, whose marriage has collapsed, or whose wife has died, who have lost their job or retired, and who decide to take time off, on the road to somewhere ancient, beautiful and reputedly holy, to sort out their lives.

The clear and the woolly, the devout and the troubled, those who know exactly where they are going and why, and those who haven't a clue, increasingly walk shoulder to shoulder along these ancient tracks.

The rise in popularity of pilgrimages in the past 80 years has been dramatic. In 1925, 90,662 Muslim pilgrims performed the Haj, but by 1995 the figure had risen more than tenfold. By December last year, it had doubled again to more than two million.

For centuries, interest in walking "the Way of St James", the 1,000 mile pilgrimage to the shrine of Santiago de Compostela in north-western Spain, the legendary resting place of St James, was on the wane: by the late Eighties only a handful of pilgrims arrived at the city's cathedral every day. But then came the revival: by 1998, the numbers had jumped from 3,500 per year to nearly 10 times that number; by 2006 they had topped 100,000.

The Kumbh Mela, the Hindu festival on the Ganges, has always drawn large crowds but today they are stupendous, the biggest assemblies of humanity ever seen in history, numbering tens of millions who are visible from space.

Also in north India, the site of Buddha's enlightenment, the bodi tree in Bodhgaya and the Mahabodhi temple that stands next to it, has attracted monks and lay Buddhists for decades - but in modest numbers. But, despite Bihar's reputation as one of the poorest and most dangerous corners of India, the crowds of pilgrims have continued to multiply. Now, more than 350,000 come every year, and the small town is crammed with monasteries, temples and meditation centres. Last month, the Indian government inaugurated a train connecting Bodhgaya with the other main Buddhist pilgrimage sites.

But it is in Europe that the pilgrimage, while enjoying a surge of popularity, has also undergone a subtle change of meaning.

In the Middle Ages, and for many believers today, a pilgrimage to Lourdes or Medjugorje was like the Haj for Muslims or a dip in the Ganges for Hindus. But the huge rise in numbers of western pilgrims today derives not from a desire for miracles, but from a need to reduce one's life to its simplest elements.

This August, Rev Edward Condry, an Anglican priest and canon treasurer of Canterbury Cathedral, is leading a group of 30 pilgrims from Canterbury to Rome by bicycle along the restored Via Francigena, an ancient network of modern roads and restored trails that in 1994 was declared a Cultural Route by the Council of Europe. "Thanks to Thomas A Beckett," says Condry, "in the Middle Ages Canterbury was one of the four great pilgrimage destinations, along with Santiago, Jerusalem and Rome. But the Reformation killed it off. Calvin's view was typical: a pilgrimage, he said, never gained anyone salvation.

"Even today, we Protestants feel strange at sites like Lourdes. But for me, the pilgrimage is the dominant metaphor for what faith is like: walking embodies the spirit of faith." Condry is also walking to Santiago, doing the 1,000-mile pilgrimage a week at a time, one week per year.

Perhaps the most truly modern pilgrimages are like those conducted by the Dalai Lama when he travelled to Lourdes and the Wailing Wall in Jerusalem, or by the Christians who travelled with him to Bodhgaya.

As Condry explains, the pilgrimage's goal is no longer necessarily the point. "Walking is such a minimalist activity," he says, "the less you have in your rucksack the better, and with this stripping away of possessions you are left startlingly exposed. And that's the significance of the pilgrimage. Reaching Santiago is important - but do I really want to reach Santiago?"