Harry visited Brockholes Nature Reserve in Preston where he saw young people taking part in conservation and bush craft activities as part of the Myplace project.
The partnership between Lancashire Wildlife Trust and Lancashire Care NHS Foundation Trust aims to improve the health and wellbeing of participants through a range of ecotherapy activities.
Based on the site of an old quarry, Brockholes has become a reserve for breeding wading birds, dragonflies and butterflies and has received more than one million visitors since it opened in April 2011.
The prince joined the youngsters, aged between 13 and 24, in the woods as he watched them create a dead hedge from branches to provide shelter for small animals.
An impressed Harry told those taking part: "A concrete jungle is not good for anyone."
He watched another group put on blindfolds to use their other senses to identify types of tree before settling down for a campfire chat over toasted marshmallows.
He declined a marshallow himself and revealed it was not something he had done himself in his childhood.
Harry said: "You are the lucky ones, getting this experience while your friends are stuck inside watching television or playing computer games."
Among those youngsters he met was Hannah Croft, 18, from Leyland, who said meeting the royal was "brilliant" and that he was a "really cool guy".
She said: "It was really good to share experiences.
"I think that the Heads Together campaign he is involved in with his brother is absolutely amazing and it was really rewarding to meet him today.
"It's very good that we have people like that in the Royal Family who are fighting for this cause."
Miss Croft has been involved with Myplace for nearly a year and said the scheme had helped her to aspire to work in healthcare advocacy.
By 2020, Myplace aims to have empowered 1,000 young people to shape and deliver environmental improvements in their communities and to have enhanced 120 greenspaces within urban neighbourhoods.