The centre is mainly used by groups from Cardiff

The extension to the Storey Arms centre, which is owned by Cardiff Council, will increase bed capacity by 50%.

Most of the cost has been met by �512,000 of lottery funding.

The centre is popular with schools for activities including mountaineering, caving, kayaking and canoeing.

The funding helped pay for expanding the number of beds from 27 to 42.

Head of centre Dave Ludlam said: "It means larger groups and more groups can come, bearing in mind our commitment to sustainability in the national park."

The facility, which was first opened by 1969, can be used by more than 4,000 people a year from schools and the wider community.

Pupils and staff from Woodland and Cantonian High Schools in Cardiff were invited to the opening ceremony.

They will also be involved in a variety of activities on the day including a demonstration of living in a tipi - a conical tent - and wall climbing.

Cardiff Lord Mayor Councillor Freda Salway, who will officially open the extension, said: "The Storey Arms Outdoor Education Centre has been a wonderful council resource for years and I'm so pleased that is being extended in such style."