Tashigang is the end of the road for most travellers in Bhutan. The Lateral Road from Thimphu and Paro takes two to three days of hard driving, breaking the journey at Bumthang and either Mongar or Yongkhola. Allow more time if the monsoon has been working on the road — landslides are routine between June and September.
The nearest domestic airport is at Yongphulla, about 25 km south near Kanglung. Druk Air and Bhutan Airlines run a small number of flights from Paro when weather and runway conditions allow, but cancellations are common and you should not plan your return on a tight schedule.
The other approach is overland from Samdrup Jongkhar on the Indian border, four to five hours south through Kanglung. This route makes sense if you are crossing in or out of Assam.