One trip that, according to Kevin Wright, is "pretty indicative of the faith-based market in North America" is Globus Journeys' most popular tour, the "Footsteps of the Apostle Paul," an 11-day excursion throughout Greece and Turkey visiting the sites of the early Christian missionary's sermons. Paul's letters (like the well-known epistles to the Corinthians) provide a foundation for the New Testament and Christian theology.

Martin Luther's break from the Pope and the Catholic Church signaled the Protestant Reformation in the 16th century. Twenty-first-century Protestant travelers can visit Wittenberg, where Luther nailed his 95 theses to the door of the Castle Church, as well as significant sites in the lives of other Protestant leaders such as John Hus and Martin Bucer. Reformation Tours' 10-day trip leads travelers through Germany and Switzerland to important sites in the history of the church.

"Jordan has in the last decade experienced a lot of growth in faith-based tourism," says Kevin Wright, adding that "Jordan's tourist board has been very proactive in getting the message out worldwide" about its religious sites. A majority Muslim country, Jordan's attractions include the tombs of Mohammad's companions and military leaders, as well as Christian and Jewish sites like Bethany Beyond the Jordan, where Jesus is said to have been baptized, and several sites relating to Moses and the Exodus, including Mount Nebo where, according to the Old Testament, the exile viewed the Holy Land of Canaan.

Last summer the Vatican inaugurated its charter-flight service for Catholic pilgrims (the plane's headrests were inscribed with the words "I search for your face, Lord"). The first flight was to Lourdes, and the Vatican says its chartered Boeing 737 now plans to fly some 150,000 Catholic pilgrims to different holy sites throughout the Middle East and Europe.

Jerusalem is Judaism's holiest city and home to a number of significant spiritual sites for Christians and Muslims as well. The Western Wall, Al Aqsa Mosque, the Church of the Holy Sepulchre and Dome of the Rock are among the most visited. According to the Associated Press, "Increasingly … visitors are devout Christians looking to follow in the footsteps of Jesus. Their trips are often organized by tour companies that cater to church groups, and their itineraries are based on stories from the Bible. They get baptized in the Jordan River, sail on the Sea of Galilee, and visit the olive grove where Jesus is said to have delivered the Sermon on the Mount."

Bodhgaya is one of the holiest cities of Buddhist faith. According to the India Department of Tourism, the Mahabodhi Temple Complex "sits on the hallowed spot where the ascetic prince Siddharth attained Enlightenment to become the Buddha and thereafter pledged his life to deliver mankind from the cycle of suffering and rebirth." Many tour companies offer Buddhism-centered vacations, or "Footsteps of the Buddha" itineraries, which include additional stops such as his birthplace, Lumbini.

Hinduism's holiest city is located on the banks of the Ganges and legend has it that the Hindu deity Shiva once lived here. An estimated one million pilgrims flock to Varanasi each year to wash away sins in the sacred river—or to die in it. (Passing on in Varanasi promises liberation from the cycle of rebirth.) Popular stops on Varanasi tours include the "ghats" or steps leading into the Ganges, and the Kashi Vishwanath Temple, dedicated to Lord Shiva.

Muslims who can afford it are required to undertake the hajj, or pilgrimage, to the Saudi Arabian city of Mecca at least once in their lifetime. Many pilgrims visit Mecca for "umra"—a trip to the holy city made outside of the Hajj timeframe. For those who have a big enough budget, the pilgrimage can become a luxury adventure. Afta Tours' "Super Deluxe Package" is listed at 5,950 euros (about $9,000).

Beyond Jerusalem's holy sites, Jewish-themed tours include "heritage" trips that highlight the history of the Jewish diaspora in different areas of the world. Atlas Cruises and Tours' Jewish Heritage Tour is a 12-day excursion that visits the former Jewish Ghetto and cemetery in Warsaw, the Jewish museums in Budapest and Prague, and the concentration camps at Auschwitz and Birkenau. Pacific Delight's "14 Day China & Yangtze River Jewish Heritage Tour" starts in Kaifeng, where a group of Jews wandering the silk road settled in the year 998 A.D.

Ireland's patron saint left lots of footprints on his native isle, and modern-day travelers often begin their "Footsteps of St. Patrick" tour at Dublin's St. Patrick's Cathedral before heading to the west of Ireland and ascending the "Croagh Patrick," where the saint is said to have fasted for 40 days and 40 nights (and where, according to legend, he subsequently banished the snakes from the country).

Each year, thousands of hikers follow the 1,000-year-old pilgrimage route to this northern Spanish city where a monk claimed to have discovered the tomb of St. James and a majestic Romanesque cathedral now presides. Santiago de Compostela became an important site of Christians' struggle against the then-Islamic state. The way of St. James is now a popular route for bicycle tours; wine and cheese connoisseurs also use the route as an epicurean pilgrimage, exploring the area's rich Galician cuisine. Cellar Tours offers customized wine and culinary trips through the region.

According to the World Heritage Center, "three sacred sites—Yoshino and Omine, Kumano Sanzan, Koyasan—linked by pilgrimage routes to the ancient capital cities of Nara and Kyoto, reflect the fusion of Shinto, rooted in the ancient tradition of nature worship in Japan, and Buddhism, which was introduced from China and the Korean Peninsula." The sites reportedly draw 15 million visitors annually. Hot springs and resorts along the way ease the journey for the contemporary pilgrim.

The Virgin Mary is believed to have appeared in 1531 to a poor Indian peasant named Juan Diego on a hill at Tepeyac, northwest of what's now Mexico City. Believers maintain that Juan's cloak was miraculously imprinted with an image of Mary's face. That cloak hangs above an altar in a basilica built on the site of Diego's vision at La Villa Guadalupe. Several contemporary tours combine Guadalupe visit with walks among the ancient holy city of Teotihuacán, home to the Temple of Quetzalcoatl and the Pyramids of the Sun and the Moon.

Visiting the Catholic holy sites of Italy is a popular faith-based tour package, and usually includes stops at St. Peter's Basilica in Rome and the 13th-century basilica of St. Francis at Assisi, in the medieval city that was the birthplace to the patron saint of animals and ecology. Classic Pilgrimages' 12-day Italy tour features a papal audience at the Vatican ("subject to the Holy Father's schedule").

Every 10 years this town in Bavaria puts on an elaborate show about the suffering, death and resurrection of Jesus Christ. The tradition started in 1633, when, in the midst of war and plague, the local villagers made a pact with God: If saved from the plague, they would re-enact the drama of the savior's life every decade. More than four and a half centuries later, they're still at it, and the next show is scheduled for 2010. Several tour companies are accepting reservations; they're combining the show at Oberammergau with other stops on Christian tours of Europe.