Ogwen Cottage at Nant Ffrancon near Bethesda was shut by Birmingham council last July to cut costs.
But it was recently acquired by National Trust Wales which said it would work with the Outward Bound Trust to "offer inspiring experiences".
The trust said an anonymous donor had helped them buy the cottage.
Trystan Edwards, the conservation charity's general manager for Snowdonia and LlÅ·n, said: "Ogwen Cottage has been the focal point for adventuring into these mountains for many years.
"We're really looking forward to maintaining this tradition and working with the Outward Bound Trust to ensure that young people get to experience this stunning corner of Snowdonia."
He added: "We're extremely grateful to an anonymous donor for helping us safeguard this very special place."
Kim Parry, of the Outward Bound Trust, said: "We look forward to welcoming many thousands of young people to Ogwen Cottage in the years to come, to experience the wonderful environment on the doorstep of the centre and to benefit from an inspirational outdoor learning experience."
Ogwen Cottage is nestled between both Carneddau and Glyderau mountain ranges right at the starting point for many popular walking and climbing routes.
It had a guide price of more than Â£375,000 when it was put up for auction last year.
It has eight dormitories and has provided holiday accommodation for city children for 50 years.
The future of an outdoor education centre in Snowdonia has been secured thanks to an anonymous donor and a partnership agreement by two trusts.