Almost as soon as Bangkok was founded, Chinatown started to form; it's the city's oldest residential neighborhood. Today it's an integral part of the city, bustling with little markets (and a few big ones), teahouses, and restaurants. Like much of the Old City, Chinatown is a great place to explore on foot. Meandering through the maze of alleys, ducking into herb shops and temples along the way, can be a great way to pass an afternoon, though the constant crowd, especially on hot days, does wear on some people.
Bustling Yaowarat Road is the main thoroughfare. It's crowded with gold shops and excellent restaurants. Pahurat Road, which is Bangkok's "Little India," is full of textile shops, some quite literally underground. Many of the Indian merchant families on this street have been here for generations.
Getting to Chinatown is easiest by boat, but you can also start at the Hua Lamphong subway station and head west to the river. The amount of traffic in this area cannot be overemphasized: avoid taking a taxi into the neighborhood if you can help it.