Going from A to B within Thailand : Taking the train
So if you like adventure and meeting locals just take the train!
The main train station for almost all Thailand is Hua Lumphon in Bangkok. From here there are basically 4 train-lines leaving in all directions of Thailand. But there is also a second train station Thonburi, located along the Chao Phraya River (other side) for the Western Line (Nam Tok & Kanchanaburi).
Trains travel both at day-time as at night. At night there are sleeping couches with First, Second and Third class. First and second class is air-conditined. In day-time there is also First, Second and Third class. Again first and second class is air-conditioned, and it is like traveling in an air-plane with a hostess for in-train service. All trains have toilets and long-haul trains also have a restaurant. For more information about the train service see Railway Thailand
The Northern Line with end-destination Chiang Mai. Traveling thru the beautiful mountains of North Thailand. This line is passing Ayuthaya, Phitsanulok, Uttaradit and Lampang.
The North-East Line with 2 different end-destinations. First the line to Nong Khai as transit point to Vientiane in Laos. And secondly to Ubon Ratchathani as transit point to Pakse in Laos.
The Eastern Line with also 2 different end-distination. First Aryanyapathet as transit point to Poi Pet in Cambodia (to go to Siem Reap). And secondly to Sathahip (passing Pattaya).
The Western Line with end-destination Nam Tok and passing Kanchanaburi and the Bridge over the River Kwai.
The Southern Line with a a few different end-destinations. First of all all the way south to the border with Malaysia Sungai Kolok. And originally also to Padang Pasar, but is seems that since March 2016 this is not done anymore. The some other end-destinations in the south are Nakhon Si Tammarat, Khiri Ratthanikham and Kantang. This line is also passing Hua Hin, Surat Thani (to go to Koh Samui) and of course Hat Yai.
Well and there are some short locals train-lines near Bangkok. And be aware that there are on the main-lines also local train-schedudles in day-time.