The National Museum

Bangkok is home to an extensive and very informative National Museum, which claims to be the largest of it's kind in all of South East Asia. It serves as a good place to learn about the full range of Thai culture, history, and of the traditional significance of Buddhism to the Thai way of life. Many of the significant remains of the former capitals Sukhothai and Ayuthaya are displayed here, and if you're planning to go to them, a visit here first should be rewarding. Depending on your interest, a visit here could take anywhere between an hour or so up to most of a day.

There are free English language tours, lasting about 2 hours, available of the museum, starting at 09.30am on Wednesdays and Thursdays. On Wednesdays, tours are also available in French and Japanese, and in German on Thursdays. These are well worthwhile, else you may not understand much about any of the exhibits and their significance especially as some of the galleries are lacking in information.

6 buildings make up the National Museum. The first building, on the left as you come in past the entrance, is the Sivamokhapiman Hall. This contains the ticket office, and the galleries of Thai history and prehistory. This includes perhaps the museum's star exhibit, the Inscription No. 1 from the Sukhothai era. Supposedly written by the great King Ramkhamhaeng himself, it is regarded as the Thailand's first work of literature. It describes the greatness and prosperity of the Sukhothai kingdom, and the benevolence of the King. All Thai school children are taught the famous opening lines, 'nai naam mee bplaa, nai naa mee kao' (ในน้ำมีปลา ในนามีข้าว) meaning 'in the water there are fish, in the fields there is rice'.
Opposite here is Buddhaisawan Chapel (sometimes known as Wat Buddhaisawan). It was built in 1787, shortly after the founding of Bangkok and contains a very revered Buddha image, the Phra Buddha Sihing. The story of this tells of it floating to Thailand from Ceylon (Sri Lanka), but it is generally thought to have originated in Sukhothai. Identical images are also found in Nakhon Si Thammarat and Chiang Mai. It remains unknown which one is the genuine original. There are also impressive murals in here, starting from the right of the back door.
Other highlights of the museum include recovered jewelry and gems, giant shadow puppets, weapons, ivory, royal possessions, musical instruments, and Asian art and antiques through the centuries. Details

Entry to the museum is 40B, and this includes a thin leaflet. A more comprehensive guide can be bought for 50B, and if you don't take a tour this is worth buying. The museum is open Wednesday to Sunday, 09.00am to 4.00pm, though tickets can only be bought until 3.30pm. It is located on Na Phra That road, next to Sanam Luang. Photography is banned inside the museum buildings.
Don't listen to anyone on the street as you try to enter telling you it's closed for a 'Buddhist holiday', 'cleaning' etc, or asking if you want to see the 'Lucky Buddha' instead - it's all part of a sophisticated gem scam. The museum is just the other side of Sanam Luang from Wat Phra Kaew and Wat Pho, and just a small boat ride from Wat Arun. Some of the other sights in the Ko Rattanakosin area are within walking distance. The Banglamphu accommodation is very close to the National Museum. The nearest river express pier is Tha Phra Chan. The buses that stop on the west side of Sanam Luang are the closest to the National Museum. These are ordinary buses 15, 30, 32, 43, 59, 64, 80, 123 and aircon bus 3

http://www.into-asia.com/bangkok/attractions/museum.php