In my experience, this is the most lively market I have ever been. It is also big and you can find lots of things here. The easiest way to get here from the city is of course via MRT or BTS. If you take MRT, you need to disembark at Chatuchak Market Station. For BTS passengers, exit at Mochit Station.The market is just a couple of minutes walk from both stations. There are also buses and taxi services available.
The market has many sections which are identified with type of things that are up for sale. It has clothing section, art, food and beverage to name a few. There is also a park (Chatuchak Park) near the market. Here are some photos: