I tried hard not to include the same country twice, but with Thailand seemingly being the backpacking centre of the world, it was not possible. I could have even potentially included Thailand to Malaysia or Thailand to Myanmar in this list as well.
5. Cambodia to Thailand, via the Poipet/Aranyaprathet crossing, might be a little infamous due to the scams that operate around here, but hundreds of thousands of backpackers do it every year.
4. Nepal to Tibet (ranks higher in term of uniqueness but due to the political instability of Tibet, not many people can undertake this crossing). The Tibetan side looks more impressive than the Nepali side.
3. Peru to Bolivia via Desaguadero must rank as one of the top crossings in the world, and the most popular in all of South America. It is the most direct route to take if you wanted to head to the Bolivian capital in the Andes, La Paz.
2. Belize to Guatemala at the Benque Viejo del Carmen/Melchor de Mencos area is an overland border crossing that almost every backpacker in the region will undertake at some point on their travels.
1. Thailand to Laos via the Mekong at Chiang Khong/Huay Xai. This one is just about more popular than the other entry in the list involcing Thailand, and it has a uniqueness about it involving a slow boat down the Mekong River to the border checkpoint. However, as of 2016, foreigners cannot cross the border in a boat, and must use land instead.