Eighteen months ago, when the New York-based T writer at large Aatish Taseer began planning his reporting trips for this month’s three-part feature story — an exploration of religious travel in Bolivia, Mongolia and Iraq — he was already well acquainted with the idea of pilgrimage. His first book, the 2009 memoir “Stranger to History,” opens with what is arguably the world’s best-known faith-motivated journey, the hajj to Mecca, and ends with what he describes as a personal pilgrimage to meet his estranged father in Pakistan. In Delhi, India, where Taseer grew up, quick trips for the purpose of worship were commonplace. “People would do a pilgrimage on an ordinary Sunday,” he says, “instead of going to an amusement park.”