Top 3 in Top 10 tourist attractions in Thailand.
Even if your plans to Thailand mostly involve frolicking on the beach and eating as much Massaman curries and Thai food as you can, you'll probably spend at least a day or two in Bangkok. There's a lot to see and do in the capital, but the Royal Palace should definitely be at the top of your list. It's the number one attraction in the city, and it's astounding in both historical significance and craftsmanship.
The grounds are a labyrinth of ancient palaces, temples and monuments, the most important being Wat Phra Kaeo (Temple of the Emerald Buddha), which is said to house a piece of hair or bone of the enlightened Buddha himself. .
Allow a few hours to do the Royal Palace's justice, but if you want to walk more then you can easily tour some of the other major city landmarks nearby. The famous Wat Po and Wat Arun, the Temple of Dawn (a great place to watch the sunset), are just minutes away.