The crossing is not difficult, providing you are not carrying a lot of luggage. From the railway station it's only a short distance by trishaw to the Thai immigration post on the border. Here porters are on hand to take you to Malaysian immigration and customs. From Kota Bahru there's a rail line that runs down the central highlands of the Malay Peninsula to Singapore. It is an exciting train trip through some dense jungle, parts of which are still unexplored to this day.
Sleepers are available for the overnight trip.
The second most popular train route in Thailand is the northern run to Chiang Mai, located in the hills 750 km north of Bangkok. The overnight express leaves Hualumphong Railway Station at 6 PM each evening and arrives in Chiang Mai at 7.40 the next day. There was a time, not so long ago, when passengers on the Chiang Mai Express had to close their compartment windows between Bang Mun Nak and Taphan Hin. It seems that when the train stopped in Bang Mun Nak, monkeys would swoop down from the trees and climb on top of the compartment roofs. They rode the train to the next stop at Taphan Hin, where they jumped off into the trees only to catch the next train back to Bang Mun Nak.