For curious kids, this is the chance to embark on the journey of a lifetime—and see how faraway countries have more in common than you might expect! Hopscotch from country to country in a chain of connecting attractions: Explore Mexico’s glittering cave of crystals, then visit the world’s largest cave in Vietnam. Peer over a 355-foot waterfall in Zambia, then learn how Antarctica’s Blood Falls got their mysterious color. Or see mysterious...