Celtica was conceived as the Welsh National Centre for the study and interpretation of Celtic culture. A major visitor centre complex was constructed by means of a substantial extension to a Grade II* mansion house (itself in need of extensive repair).
Arrol and Snell acted as lead consultant and was involved in all aspects of the design and management of the project. The interpretative designer was John Sunderland and innovative audio-visual techniques were used throughout. The major part of the exhibition was in a purpose-designed extension and the main house became an education and study centre. The project also included extensive access improvements.
The rehabilitation of the old house (Plas Machynlleth) was a major regeneration scheme for the town and created a significant economic improvement by boosting tourist revenues and visitor numbers in the region.