Traveling to Bhutan via Kolkata (by train) involves a combination of train and road travel due to Bhutan's landlocked location and limited transport infrastructure directly connecting to India. Here's a general outline of how you can plan this journey:

Step 1: Kolkata to Hasimara (By Train)

1. Book a Train Ticket: Start by booking a train ticket from Kolkata to New Alipurduar or New Jalpaiguri. These are major railway stations near the Bhutan border.
2. Popular Trains: Some popular trains from Kolkata to New Jalpaiguri include Darjeeling Mail, Kanchanjunga Express, and Uttar Banga Express. For New Alipurduar, you can consider trains like Padatik Express or Kanchankanya Express.
3. Travel Time: The travel time can vary depending on the train and route, but it generally takes around 8-12 hours from Kolkata to New Jalpaiguri or New Alipurduar.

Step 2: New Alipurduar or New Jalpaiguri to Jaigaon/Phuentsholing (By Road)

1. From New Alipurduar:Once you reach New Alipurduar, you will need to take a taxi or a shared jeep to Jaigaon, which is the town on the Indian side of the Bhutan border.Jaigaon is located next to Phuentsholing, the Bhutanese counterpart across the border.
2. From New Jalpaiguri:From New Jalpaiguri, you can also take a taxi or bus to Jaigaon/Phuentsholing. Buses and taxis are readily available at New Jalpaiguri station for this route.

Step 3: Crossing the Bhutanese Border

1. Entry Formalities: At Phuentsholing, you will need to go through entry formalities to enter Bhutan. This includes obtaining a permit, which can usually be arranged through a Bhutanese tour operator or at the permit office in Phuentsholing.
2. Permit Requirements: Ensure you have all necessary documents for the permit, including a valid passport (with at least 6 months validity) and any required visas depending on your nationality.
3. Travel Restrictions: Note that independent travel in Bhutan is not permitted; tourists must book their travel through authorized tour operators.

Additional Tips:

• Accommodation: Book accommodation in advance, especially during peak tourist seasons, as availability can be limited.
• Currency: Bhutan's currency is the Bhutanese Ngultrum (BTN). Indian Rupees (INR) are widely accepted in Jaigaon/Phuentsholing, but it's recommended to exchange some money to Ngultrum for convenience in Bhutan.
• Altitude: Be mindful of altitude changes if traveling to higher altitude destinations in Bhutan. Acclimatize gradually to avoid altitude sickness.

Conclusion:

Traveling to Bhutan via Kolkata (by train) involves a scenic journey through West Bengal's landscapes followed by a road trip to the Bhutan border. It's a unique way to experience the journey to this beautiful Himalayan kingdom. Ensure you plan ahead, especially regarding permits and transportation from the border into Bhutan. Safe travels!