The 280km climb towards the Bolivian border provided a very noticeable change in culture. We left the hustle and bustle of city life in San Salvador de Jujuy to find ourselves, three days later, witnessing a sheep competition in a very Bolivianesque village. There were several Crufts-style awards including "best in show," in addition to other categories such as "best meat." Exactly how the latter category was judged confused us a little given the eventual winner was still happily wandering around the enclosure! During this stage of the trip, which followed the sadly redundant railway line built by the British at the end of the 19th Century, we entered the Tropics by crossing the line of latitude called the Tropic of Capricorn. This, for the astronomically-inclined amongst us, marks the most southerly point where the sun can appear directly overhead at noon.

The gain in altitude, from 1200m to almost 4000m, made the cycling gradually more tiring and the three of us found ourselves breathing a lot more intensely as we passed the 3000m mark. As a result, a day off in the Argentinian border town of La Quiaca (exactly 5121km from our start-point in Ushuaia according to a road sign) provided a welcome break, as well as an extra day's acclimatisation, before we got our passports stamped once more as we entered Bolivia.

The arrival in Bolivia signalled a switch back to bad roads, which when combined with rain, can become like a mud-bath. Fortunately, we avoided any downpours and arrived in the town of Tupiza after one day. A lack of a supermarket made the purchase of supplies tricky as it involved visiting several different little shops and almost two hours of asking where we could buy basic necessities such as bread. Eventually, we found the three nights/mornings worth of pasta/oats and four days worth of bread and tuna ready for the cycle to Potosi.

The route was extremely hilly with regular 400-500m climbs quickly eradicated by a similar size descent. The villages we passed on this stretch appeared very poor and almost all of them had erected boards giving thanks to organisations such as "US Aid" for providing the funds to build schools, provide water etc. etc. Despite the obvious lack of material well-being, we've found the Bolivian people to be some of the friendliest of the trip so far. Stops at road-side cafes provide us with the chance to interact with the local villagers as well as chat to passing lorry drivers. These lorry drivers can provide useful information on the road ahead and we were particularly happy to hear that a new asphalt road was under construction. This meant we had several hours of smooth cycling on a road not open to traffic yet. The only downside was every so often having to negotiate a wall of gravel, which accompanied a "Diversion" sign. However, we reckon this provided good obstacle training for "Military Man West" as we've nicknamed him.

The arrival in Potosi, officially the world's highest city at 4,070m, was spectacular as we cycled beside Mount Cerro Rico. An abundance of silver deposits in the local vicinity once made Potosi the richest town in the world until the British arrived and the "English Pirate", as the locals here refer to him, Sir Francis Drake took most of it from the Spanish. Nowadays, mining remains the principle industry of Potosi but the minerals that can be excavated are less valuable and include mainly zinc and tin. The lack of available investment to build smelting plants means most of the value-added and, hence, profit from the mining is derived by firms in the US and Europe and not the workers' cooperative here in Potosi. The average miner, we learned on our tour, can expect to earn about 1500 Bolivianos a month; that equates to roughly US$200. Working conditions are unpleasant to say the least. Two hours in the gaseous, carcinogenic and cramped tunnels was more than enough for me and this pales into insignificance when compared to the seventy hours a week worked by the average miner between the ages of 15 and 55. Efra, our guide, explained that accidents involving dynamite and collapsing tunnels are fairly common too. Overall, a life in the mines unsurprisingly shortens one's life expectancy. However, with little other choice for the men of Potosi to support their ample-sized families, many make the walk to the miners' market every day to recharge their head torches and stock up on dynamite.

The other notable feature of Potosi life has been the abundance of street protests. Bolivia holds the world record for the number of regimes in recent years and this doesn't surprise us with schools providing excursions that teach the children how to protest. Unfortunately, the combination of this with the readily available dynamite in the miners' market meant Rob had another "military" experience as we made our way home from a restaurant. Students, protesting about the closure of their university, waged battle against the riot police with dynamite grenades, which shook some of the buildings we were in. The streets were full of tear gas as the police fought back. Needless to say, we made a quick return to the relative sanctuary of our hostel where we've left the bikes to do a bit of travelling around Bolivia by bus with Dave's girlfriend, Hannah. Next stop is the salt flats of Uyuni where we'll upload some photos of our mining experience in Potosi.