One of the largest environmental projects in the UK, with a lecture theatre's walls built out of soil, has begun in mid Wales.
An artist's impression of how the centre will look when finished
The £5m education building at the Centre for Alternative Technology (CAT) is expected to create 20 jobs.
The education centre at Pantperthog, near Machynlleth, is being built to keep pace with the sustainable living charity's growing range of eco courses.
Funded by public and private money, it will have a 200-seater lecture hall.
Preliminary works are under way at what CAT is calling its Wales Institute for Sustainable Education (WISE) and building work is expected to follow later this year.
CAT describes it as one of the largest construction projects of its type in the UK.
Students at the institute will study courses including wind power, solar water heating, organic gardening and blacksmithing.
A circular lecture theatre will be made from a rammed earth system like that used in Cornwall's Eden Project.
Project manager Philip Horton said 300 tonnes of soil, with a high clay content, would be used to build the circular lecture theatre.
The rammed earth process has been used at CAT before
"We will erect the wall in sections," he said. "There will be 190 blocks weighing 1.6 tonnes each, measuring two metres long, one metre high and half-a-metre thick.
"The outside will be varnished and depending on the soil it could bring out a nice red finish."
The soil will be rammed by a pneumatic machine to compress it into solid blocks.
The process is based on technology developed hundreds of years ago in the south-west of England, which saw cow manure, soil and straw mixed to build homes.
"The Eden Project in Cornwall has used a similar rammed earth system to build some of its walls," said Mr Horton.
Rammed earth reduced the impact on global warming compared to using cement based building products, added Mr Horton.
Among the scheme's public backers are the European Union (£1.2m), the Welsh Development Agency (£450,000) and Powys Council (£700,000).
Its private financers include UPM Kymmene UK (£75,000).