The best way to get there is by the skytrain. You can buy a day ticket for 130THB in every station. The market is situated near the 'Siam' station next to the parc. You better schedule Several hours for a walk through this market as it's pretty big. We've walked for more then 3 hours and only saw the biggest road without entering all the small allies.
It's really worth visiting when you want to see the real Thai people and to buy a local product. From food to clothes, you can find it all for very little prices.
A nice cotton T-shirt from good quality (although this is what it seems to be), is for sale for 150/300 THB.
