Because Bhutan has no domestic air facility, doesn’t yet possess any helicopters and does not have a centimetre of railway track, the only way to see the kingdom is either by foot or by road. There is one main road: the National Highway, a 3.5m-wide stretch of asphalt that winds its way up and down mountains, across clattering bridges, alongside the side of cliffs and over high mountain passes. Rivers, mudflows and rock fall present persistent hazards, especially when it rains. The road can easily become blocked due to snow or landslides and can take anywhere from an hour to quite a few days to clear. Unless you want to walk, the only way to tour between towns in the south of Bhutan is via India, because there are no roads. At present this is impractical for foreigners since the only road entry point that foreigners are allowed to use is Phuentsholing. Tour organizers use Japanese-made buses, minivans and cars, depending on the size of the group. These vehicles can take you about anywhere in the country, but for trips to central and eastern Bhutan during winter (December to February) or the monsoon (June to September) a 4WD vehicle is an advantage, and often a requirement.