It is summer, and as the fortunate among us head to familiar summer haunts—redolent with the smell of hedgerows and the feeling of warm earth under bare feet, once again appreciating sundown and turning the pillow to the cool side—it seems apt to reflect on the many ways in which travel is something quite qualitatively different from movement through space.

Try everything once except folk dancing and incest. This oft-quoted advice is harder to follow than you’d think.