One can enter Bhutan directly by flying to Paro International airport or travel by land to Bagodogra airport, or nearest train station at Hashimara India which is around an hour drive to reach Phuentsholing Bhutan. 

It takes 5 hours from Bagdogra to Phuentsholing approximately which is around 170 km. 

Flying to Paro Bhutan

The flights operates through sectors like Singapore, Bangkok, Delhi, Calcutta, Mumbai, Kathmandu, Dhaka and Guwahati. 

The flight takes you through some of the highest mountains in the world.
One can enjoy the view of Mt Everest, Kanchenjunga, Makalu, Lhotse to your flight to Bhutan. 

Travel by Land to Bhutan

The Tourist can enter either by Phuentsholing, Gelephu or Samdrup Jonkhar.
Phuentsholing is mostly used by the tourist entering by land to Bhutan and it is around 170km from Bagdogra airport. 

It takes approximately 5 hours to reach and after processing your permits at immigration it is another 5 hours drive to reach Thimphu. 

Samdrup Jonkhar is another sector to enter Bhutan. It takes you through Trashigang, Mongar, Bumthang, Trongsa and then to Thimphu which usually takes three to four days.
Gelephu, Tourist entering by this sector will take nine to ten hours to reach Thimphu and it passes through sub-tropical areas of Bhutan.