This is the weirdest way we have ever crossed a border, and also the most physically challenging.
It involved a 3 hour boat journey on a boat that goes twice a week until April when it stops for the year, to a small harbour called Candilario Mansilla above which one family have some land, a house, a campsite and some solar panels. Two people live there all year round and the rest of the family leave for the winter. This is a hard place to survive! We arranged for a horse to carry our bags over the pass the following morning and that we would push our bikes and trailer containing Leo.
1km from the harbour there is a seasonal Chilean border post reached via a steep, rocky, 'road' which allowed cycling for about 5% of the time, the rest involved just pushing. After the border post the road climbed steeply for 4km and was more or less impossible to cycle. For the following 10km we were able to ride as the track improved and passed through gently sloping fields and forest.
We then reached the actual marked border (where we had lunch between the Argentina and Chile signs so that Leo could have his first meal in no-man's land) and the track became a very difficult 6km single path into Argentina, up and down through forest, winding around roots and between trees, over rocks, crossing streams and even through occasional boggy areas. We had to lift the trailer to get it around and over obstacles while amazingly Leo either giggled or slept through the chaos. At times he was stuck in mud or sat in the middle of a stream while we grunted and swore, trying to stay dry or upright.
The last section down to Lago del Desierto was madness, a path deeply eroded into the hill, only as wide as the trailer, dropping steeply and winding constantly. We could let go of the bike and trailer and it just stood there wedged between the sides of the path. Leo woke up for this bit, and seemed very interested in some of the angles that he found himself at.
Finally after 4 hours of struggle we reached the shoreline and the Argentinian border post only to see a storm blowing our way across the lake, our only route to more food and eventual civilisation. The horse arrived a couple of hours later with our bags. We had done it!