Fly into Bangkok International Airport.
Take a taxi to the Hua Lamphong Railway Station.
Board a train for Nakhon Si Thammarat, one of the southern provinces on the eastern shore of Thailand.
Take a bus from Nakhon Si Thammarat to Krabi.
Go to Singapore International Airport.
Take a taxi to the KTM Railway Station.
Purchase a train ticket for Kuala Lumpur. When crossing over from Singapore to Malaysia, the train will stop, you will go through customs and then reboard the train.
Arrive in Kuala Lumpur and purchase two tickets: one from Kuala Lumpur to Penang, Malaysia, the other from Penang to Traing, Thailand.
Arrive in Penang and board the train to Trang. The ride from Kuala Lumpur to Penang can be long (around seven hours), so most often the train from Penang to Trang will be the next day.
Purchase bus tickets from Trang to Krabi and board the bus.