Doi Inthanon is the highest mountain in Thailand, and on cool-season mornings there is frost on the grass at the top. It stands 2,565 metres up in the hills west of Chiang Mai, and the road climbs out of one climate into another. Tropical foothills first, then Wachirathan falling white through the trees, then forest turning mossier with every switchback until the air is cold enough to show your breath. At the top there is a sign and a stupa holding the ashes of Inthawichayanon, the ruler of Chiang Mai who spent his final years trying to keep the northern forests from the axe. Beside it a wooden boardwalk loops around the Ang Ka bog. Moss hangs off every branch, ferns crowd the rail, and the peat underfoot stays near 10°C all year, the coolest and wettest ground in the country. If you stand still, the branches fill with Himalayan birds barely found elsewhere in Thailand.
Kew Mae Pan starts a little below the summit. The loop runs two or three hours through alpine grassland and mossy cloud forest, always with a guide from the Hmong village below, and it ends at a cliff edge where the ground simply stops. People walk it in the dark to be there at first light, when the valleys are full of cloud and the ridges of northern Thailand come up out of it pink, then copper. Lower down stand two chedis, Naphamethanidon and Naphaphonphumisiri, raised by the air force rather than any temple, for the king's sixtieth birthday in 1987 and the queen's in 1992. Terraced flower beds tumble down the slope between them, full in the cool months of blooms the lowlands are too hot for. The same cold made the villages below. Karen and Hmong families here grew opium poppies into the 1970s, and what replaced them came out of a royal project begun in 1969: coffee, and fruit that needs a cold night. The mountain that frosts its own summit has those to spare, and the coffee you drink at the top was grown on the slope you came up.