These photos were taken at Portmeirion during low tide in the bay.
It is possible to walk across this bay when the tide is lower.
As you can see from the pics, the sand is indeed very clear as the name of the locality would suggest.
Portmeirion itself is located in Snowdonia. Snowdonia (Welsh: Eryri) is a mountainous region in north Wales and a national park of 823 square miles (2,130 km2) in area.