Spiritually motivated travel is perhaps the oldest form of tourism. In Greater China, Taiwan remains the most vibrant religious culture centre, where centuries-old folk temples, especially in Tainan and Lugang, add colour and beauty to urban landscapes. Taiwan's tourist industry is booming - international arrivals more than doubled to 7.31 million from 2006 until last year - and religious sites have reported growing numbers of visitors from Hong Kong, the mainland and Singapore. The monastic and educational complex at Dharma Drum Mountain (DDM), 23km northeast of central Taipei, received about 12,000 non-Taiwanese visitors last year, says Bhikkhuni Guo-jiann Shih, director of DDM's department of international relations and development. DDM is also the global headquarters of a Buddhist foundation with affiliates in North America, Britain and Hong Kong. According to Bhikkhuni Guo-jiann Shih, non-Taiwanese visitors are especially interested in tours of the complex, retreats and how the Chan form of Buddhism is practised. At the end of 2011, another of Taiwan's major Buddhist organisations opened to the public what is perhaps the island's most striking religious monument. Fo Guang Shan's Buddha Memorial Centre houses a tooth, which the faithful believe was retrieved from the ashes after Buddha was cremated in 543BC. The centre, which cost an estimated US$300 million to build, welcomed 8 million visitors last year. At the original monastery next to the centre, monks, nuns and volunteers gave guided tours to more than 240,000 people last year, including more than 150,000 from the mainland. Tourists from different backgrounds tend to ask different questions. A volunteer says: "Westerners have asked me about nuns' and monks' celibacy. Ethnic Chinese would never do that, perhaps because they already know the answer." What some claim to be the biggest regular religious event in the world outside India begins and ends each spring in Dajia, a town in Taichung - Taiwan's third-largest city and now linked to Hong Kong by twice-daily flights. To mark the birthday of Mazu, the sea goddess known to Cantonese speakers as Tin Hau, an immense procession sets out on foot from Jenn Lann Temple and marches southwards. Over eight days, a palanquin bearing the shrine's revered Mazu icon is carried 300km through towns and villages, stopping en route to accept offerings at shrines. At Fengtian Temple near Chiayi, the palanquin turns around and begins the return leg. Some devotees walk both ways, and more than 1 million people spend a few hours watching or joining in. Not all of the latter are fervent believers; many are drawn by traditional puppetry and opera shows, martial-arts demonstrations and lion dances. Outsiders can seek the goddess' blessing by prostrating themselves on the road so the icon is carried over them. This pilgrimage is now promoted as the Taichung City Mazu International Festival. Throughout Taiwan, Chinese-speaking travellers are often able to stay in temple dormitories. Such accommodation is spartan but inexpensive - often no payment is required, but making a donation is customary. No more than one in 12 Taiwanese is Christian, and for many island residents, ecclesiastical architecture is exotic and appealing. One of Taiwan's most visited churches is also its oldest. The 150-year-old Wanjin Basilica, which stands in a tiny town in southern Pingtung county, is a Spanish-style church similar to many places of worship in the Philippines. Taiwan also has Catholic churches that resemble Taoist temples, and chapels designed by Pritzker Prize winners I.M. Pei and Gottfried Boehm.