In the United States, the longest continuous route is between northern California to Maine and is about 3,527 miles long, and if set out on foot, it could take anywhere between six to eight months to cover that distance. On the contrary, the shortest route between any two states is between California and Georgia; the space is about 2,339 miles. So if you try walking from one of these two states to the other, you could cover the distance anywhere between three to five months.
However, when you look at the complete picture of the world, there are more extensive stretches of land separated by various water bodies. Therefore, embarking on the journey from one part of the planet to the other may take years to complete. For instance, the distance between Argentina and Alaska was first covered by an Englishman, George Meegan, previously a sailor. He started his 19,019-mile journey in 1977 and completed it in 1983, taking over 2,425 days to cover the distance between the two. Likewise, thirty-five years later, another adventurer, Holly Harrison, who previously served in the US Army Ranger, covered the same distance following a shorter pathway in under 530 days.
These are distances that can be easily covered on foot, considering they were vast stretches of plain land or routes that can be covered on foot. Now imagine if the large distances shadowed with inhabitable and dangerous mountains like that present in Central Asia could be covered on foot; how far could you go without passing any water body?
In 2018, a combined study by the Collins Aerospace Applied Research and Technology in Cork of Ireland and the IBM Research Center of India, researchers calculated the longest possible straight route coverable on foot, without any hindrance from water bodies. This study considered the distance between China and southern west Portugal. The 6,984-mile route would cover China, Mongolia, Kazakhstan, Russia, Belarus, Ukraine, Poland, the Czech Republic, Germany, Austria, Liechtenstein, Switzerland, France, Spain, and Portugal. As expected, it would take years to complete the journey on foot.