Travel books are extremely diverse. Some are barely identifiable as travel writing. Gerald Durrell is thought of as an eccentric naturalist but in fact his books are engaging books on travel with a special focus on animal life. The kinds of travel literature, or indeed travel writers, can be broadly categorized. Top of the list are travel writers who are travelers by occupation and writers by profession. Three such writers are Paul Theroux, William Least Heat-Moon and Bill Bryson. It is probably no surprise that writers in this sub-genre are often short-tempered about travel and indeed the act of travel writing. More writers in this category are Jan Morris and Eric Newby. Once again there is a cross-over, because Morris is known as an historian and Newby as a novelist. It seems as soon as you write anything other than travelogues you have lost your purity!
Then there are travel works that are more along the lines of essays, such as V.S. Naipauls India: A Wounded Civilization, in which a journey becomes the peg on which to hang reflections and considerable philosophizing about nations, people, politics and culture. Another such work is Rebecca Wests work on Yugoslavia...