One of the three pitches has an all-weather surface and is fully floodlit, while the main building houses two administration and training blocks - one specifically for the use of Gatland and his backroom team - changing rooms, team rooms, a fully equipped gymnasium and an indoor artificial pitch.
"As a one-stop facility, this is absolutely fantastic," Gatland added.
The senior team has been based at the Vale Resort for several years.
But the major new investment has transformed the facilities into a bespoke and exclusive centre of excellence purely for Welsh international rugby use.
The Sports Council for Wales has invested £1.5m of National Lottery funding and the WRU the remainder plus running costs.
WRU group chief executive Roger Lewis welcomed the cross-agency co-operation that has seen the facilities at the Vale transformed.
"I want to thank the Sports Council for Wales and the Welsh Assembly Government for sharing our vision and closing the circle of strength and co-operation, which has made this all happen," Lewis said.
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