When ascending Phu Si from the northern side, stop at Wat Pa Huak, one of the oldest wooden wat in the city. The gilded, carved front doors are usually locked but an attendant will open them for a tip. Inside, the original 19th-century murals show historic scenes along the Mekong River, including visits by Chinese diplomats and warriors arriving by river and horse caravans. See if you can spot the mule relieving itself!