It took seven years to complete this film.
There were over 40 interviewees related to the 1960's and 1970's expeditions.
The movie was shot in different stages. The first one took a month and had all the interviews in Ecuador. The second stage had all the interviews in Argentina and U.S. The final stage had 4 expeditions to the famous Tayo's Cave and to the coordinates of what Hall claimed to be the second cave.
During the second expedition to the cave, a huge storm created a waterfall inside the cave that passed next to the crew's camp scaring everybody. In the third expedition, a similar storm ruined some drone batteries left in a pelican case by the entrance of the cave.