But as transfixing as the market is, tear yourself away by 10:30 for the 15-minute drive to your next stop, the Grand Palace, a vast compound of palaces and temples, one of which holds the country's most important image, the Emerald Buddha. (First, though, a warning: This time of day is not for the heat-shy—there's very little shade to be had. The crowds, however, are much thinner, and you'll be able to move at your leisure.)

Built in 1782, the year modern Bangkok was founded, the Grand Palace was for almost 150 years the seat of both the national government and the king's residence (parts of it are still used for various state functions). Your first stop is the Wat Phra Kaeo Museum, wherein resides a small, well-presented collection of royal treasures, including intricately worked betel-juice bowls and coins from the kingdom of Siam (1768–1932), the precursor to modern Thailand. After exiting the museum, you'll walk down a short pathway to the Temple of the Emerald Buddha, which is busy with more than a hundred buildings and stupas, most of them blindingly gold and all of them fantastically vibrant. One of the most brilliant is the Phra Mondop library (pictured bottom right), which houses sacred Buddhist texts. You'll then walk under the scaffolding (renovation work on the sanctuary began recently) into the Emerald Buddha Pavilion. Cameras aren't allowed here, but at any rate, you will be too dazzled by the splendor of the room to care. As you gaze variously upon the floor (which is lined with marble), the ceiling (lacquered a glossy red), and the walls (painted with scenes from the Buddha's life), it is difficult to keep from thinking of the Sistine Chapel, another monument to another of the world's great religions. In the front of the room, sitting on a shining throne, is the Buddha. Made not of emerald, as the name suggests, but rather of jade, it stands a surprisingly small two feet tall and is colored a dark forest green. The exact place and date of origin of Thailand's most iconic sculpture are unknown, but it is generally thought to have come from the northern part of Thailand in the early 1400s, after which it spent more than two centuries in Laos before being brought to Thailand by King Rama I in 1778. (Ask both your Bangkok guide and, later, your Luang Prabang guide to tell you the story of how the Emerald Buddha made its way back to Thailand; their answers will speak volumes about the two countries' lingering historical resentments toward each other.)

A few more minutes wandering the palace grounds and you'll be ready to faint, though whether from hunger or the heat will be hard to say. Fuel up and cool down with a cheap meal at the nearby S&P (entrées, $6–$12), where you should chase your (highly addictive) sticky rice and mango dessert with an icy glass of refreshing lemongrass juice. Fed and watered, you're off for a boat ride down the Chao Phraya, the city's wide, busy waterway. You and your guide will clamber into one of the long, flat boats you saw at breakfast, and then buzz down either Bangkok Noi or Dao Kanong canals for a tour of the city's "water streets," neighborhoods of houses whose facades front the street and whose back porches face the water. As you cut through these narrow channels, past wooden houses on stilts and plumeria trees made colorful by great bursts of vanda orchids, you're reminded of how much all of Southeast Asia prizes and depends on proximity to great bodies of water: Homes are built on it, goods are conveyed down it, and rice, the principal crop, swallows many tons of it. You'll stop next at the Royal Barges Museum, where you can admire the ceremonial boats—some of which were once used for battle—before climbing back into the boat to complete your 40-minute ride.