To raise funds for Teenage Cancer Trust, I'll be trekking through tropical rainforest in Colombia - to the "lost city". The ruins of the city of Teyuna date back 1,500 years and are now cloaked by the forest. The ruins lie in the Sierra Nevada de Santa Marta mountains, a UNESCO biosphere reserve.

Conditions will be hot and humid, and the path will sometimes take us though almost impenetrable jungle. The final approach to the city is via 1200 stone steps rising though dense vegetation.

Teenage Cancer Trust so that young people do not have to face cancer alone - to give every young person facing cancer the best care and support. This is my 21st trek for this amazing charity.