Bhutan's remote location and mountainous terrain place some considerable constraints on travel and transportation, as does the country's strict tourism policy aimed at regulating tourist arrivals so as to preserve its unique identity and traditions
Paro has the only international airport of Bhutan and is well connected by flights from Delhi, Kolkata, Kathmandu, Bangkok, Dhaka, Gaya etc.
Flights from Bagdogra to Paro take 30 minutes. From Kolkata to Paro, it takes 1hr 15minutes and from New Delhi to Paro, it takes 4hr 20minutes.
If you wish to travel by road, you will get total three border points in India for crossing over to reach Bhutan. One is Jaigaon/ Phuentsholing in West Bengal and the other two are Bongaigaon/ Gelephu and Darangamela/ Samdrup Jongkhar in Assam.
Out of the three border points, the Jaigaon/ Phuentsholing Border is the most preferred by travelers. It is easily accessible and there are facilities for staying as well as obtaining an entry permit here easily. Jaigaon is the Indian side of the border while Phuentsholing is the Bhutanese side.
Many day-trains as well as over-night trains run from Kolkata to Siliguri and also further ahead to Falakata (both in West Bengal). After reaching Siliguri or Falakata, you can hire a private taxi to Jai Gaon which is the Indian border town to cross over to Bhutan's Pheuntsholing.