A limousined coach eases out of Hanoi at dawn and the city's humidity peels away into open rice plains and limestone towers. By mid-morning the bus threads narrow country roads; the Ngo Dong river dares you to slow down as sampans slip into cave mouths and karst cliffs loom like carved walls. At Bai Dinh, bronze Buddha and rows of La Han statues give scale to a sprawling temple complex; in Trang An a two-hour boat ride winds through tunnel caves and grottoes recognized by UNESCO. Higher up at Mua Cave, a near-vertical stair of about 500 steps rewards breath with a near-circular panorama of Tam Coc’s patchwork fields.