In the past an optional cocaine making demonstration was offered on the Ciudad Perdida trek.
This is no longer a part of the trek.
The demonstration involved being taken to a hut in the jungle. The guide showed you the cocaine production process which includes obvious ingredients like coca leaves, water and some lesser known ingredients like petroleum, sulphuric acid, toilet cleaner and paint stripper.
Guides on the trek say that after photos of the production facilities were posted on the internet then military personnel were sent in to go undercover on a tour and find out the locations of the facilities.
Once they were discovered they were destroyed. The government says that it wants to keep the image of the trek and Colombia itself clean. It also says that it wants to make sure the trek is as safe as possible.