One can enter Bhutan by air or by road via private car, public bus and train. Paro International Airport is the only entry point to Bhutan by air. It is located in the south west of the country and served only by the country's flag carrier Druk Air. Druk operates four planes which fly routes to Bangkok inThailand; Delhi, Kolkata, Bodhgaya/ Gaya, Bagdogra, Guwahati in India; Kathmandu in Nepal; Dhaka in Bangladesh.
If you come by road via private car , there are three land border crossings located along southern border to India only. Phuntsholing in the west, Gelephu in the central region and Samdrup Jongkhar in the east. No border crossings are open along the Chinese northern border. Road permits are also required; however, these are processed by your local tour operator, along with your visa.
If you are planning your trip by road via public bus , you can get public buses from Kolkata, Siliguri to Phuentsholing/Jaigaon. One can easily get private buses and shared taxis from Phuentsholing to Thimphu, but a comfortable option is to book a Bhutan Post bus, which leaves each morning at 7 AM (Bhutan time) from the post office. Public buses from Kolkata depart from Kolkata's Esplanade bus station at 7PM on Tuesday, Thursday and Saturday and from the Phuentsholing Bhutan Post office at 3PM on Monday, Wednesday and Friday. The journey takes around 18 hours. Public buses from Silguri to Phuentsholing/Jaigaon depart from across the main highway from the bus station, near Heritage Hotel, at 7:30AM and 1:30PM daily. It is roughly a four hours journey. The buses are comfortable and operated by Royal Bhutan Government.
If you are planning your trip to Bhutan via train, Hasimara, New Jalpaiguri Station (NJS) and 'New Alipurduar' (NOQ) are the nearest railway stations as Bhutan has no railways. Hasimara on the main Kolkata/Siliguri line to Assam is the nearest railway station to Phuentsholing, 17 km away. Indian Rail operated train #13149 and #4084 stop here. As of October 2010, some sections of the road from New Jalpaiguri/Siliguri to Phuentsholing are in a very bad shape. Extending travel by train till Hasimara would save your freshness for Bhutan. New Jalpaiguri Station (NJP) in Siliguri is a popular choice for travellers heading to Bhutan by land. There are direct shared taxis from NJP to Jaigaon or there is the option of buses from Siliguri bus station. A taxi between the station and the bus station costs around 80rs max. Alternatively you can also take a local train to Hasimara which costs around Rs40 and takes around 3 hours. Trains from NJP should be booked ahead, as it is a popular stations amongst locals. There are not any trains leaving from this station with a tourist quota. 'New Alipurduar' (NOQ) railway station is a better option than New Jalpaiguri if you want to reduce your road journey to Jaigaon. From here, Jaigaon is only about 60 kms and can be covered in about 1 hour 15 minutes by a direct taxi. Alternatively, bus services from New Alipur Duar town to Jaigaon are also available. Most of the trains going to Guwahati stop at this railway station. It is also a shorter route for those coming from Guwahati or other north-eastern states of India.