If you have plenty of time and not much money or if you want to experience the Thai culture up close, you may want to take the train. Otherwise, it is both faster and easier to fly. Even the buses are somewhat faster than the trains.
You can travel by train from Bangkok to Chiang Mai in the north, to Isaan in the east and down south to Malaysia - and indeed even through Malaysia and all the way down to Singapore. However, you cannot travel all the way to the resort island Phuket by train. If you want to go to Phuket, you will have to switch to a bus on the way. You can, for example, switch to a bus in Hua Hin or in Surat Thani.
In Thailand, they divide the trains into three classes: First class sleeping carriages with 2-berth compartments and air conditioning. Second class is available as sleeping carriages with berths along the aisle with air conditioning or as regular seats with air-conditioning. However, there are also some second-class carriages, which do not have air conditioning. Third class has ceiling fans and open windows instead of air conditioning, and those trains usually stop at most stations - and for a long period.
The seats in all classes are very comfortable and with plenty of space. The prices are more than reasonable, even for first-class trains. For example, the 750 km (466 miles) long trip from Bangkok to Chiang Mai costs less than 1,500 baht ($43/€39/¥287/руб 2.713) in a first-class sleeper carriage. It costs less than 900 baht ($26/€23/¥172/руб 1.628) in a second-class sleeper carriage. Should you opt for the least expensive class, you will have to pay less than 300 baht ($9/€8/¥58/руб 543) for a third-class seat in an ordinary train.
The carriages on all classes are generally both old and worn out. However, change is coming - slowly. The State Railway of Thailand has bought 115 modern train carriages from China, in which you will find seat-mounted multimedia consoles in the first-class carriages, offering movies and music. In the second-class carriages, you will find large public screens.
The State Railway of Thailand will deploy the new carriages between August 2016 and September 2017. You will find them on the routes between Bangkok and the following cities: Chiang Mai, Hat Yai, Nong Khai, and Ubon Ratchathani.
Express at 62 km/h (39 miles/h)
Do not be fooled by the fact that The State Railway of Thailand uses the term "express train". It only means that the train does not stop as often as other trains. The average speed for the express train on the 12-hour-trip (according to the schedule) from Bangkok to Chiang Mai is about 62 km (39 miles) per hour.
And that is if it keeps to the schedule, which it very seldom does. I have yet to experience a train that arrived on schedule, the shortest delay on my trips between Bangkok and Chiang Mai is over an hour.
It is my impression that they run the trains according to a calendar rather than using a clock. If you travel by train, do not plan the next leg of your travel according to the scheduled arrival time. Make sure you have plenty of time for a possible delay.
Generally, I would say that you should not take the sleeper train unless you want to avoid paying for a night at a hotel or a guesthouse while travelling at the same time. The trip is both boring and uneventful.
That goes for the second-class train during the day too, although here you can enjoy the fantastic scenery along the way.
However, if you travel on third class in a non-express train in the daytime, the journey can be exciting and interesting. This way, you will experience the Thai culture up close. In addition, you will be able to enjoy the beautiful scenery along the way, and you can take photos without a limiting window.
The passengers on third class are overwhelmingly Thai. You will find that the train stops for a long time at each station, where hordes of vendors will board the train to hawk food, candy, newspapers and drinks for the travellers. That repeats itself station after station.
Please be aware that if you want to use the restroom on the train, you risk getting a surprise in the form of a toilet without a basin. The toilet at the photo below is a traditional Thai toilet that practically merely consists of a hole in the floor.
Try it, if you are adventurous, otherwise quickly close the door and try the restroom on the other side of the aisle; here you will probably find a more familiar looking toilet. In both cases, you should be aware that there might not be any toilet paper. Use the bum gun or bring your own package of paper handkerchiefs.
Usually, you do not have to book seats for a trip, unless you travel during a Thai holiday.
If you want to travel by train in Thailand, please visit the site Train travel in Thailand. Here you will find an abundance of information about the prices, how to buy tickets, routes and travel plans, and you will find many pictures of the different types of train.