Metallica's James Hetfield Welcome to Mykonos ... Enter Sand, Man!!!

Metallica's lead singer and rhythm guitarist had one thing on his mind while vacationing in Greece -- nothing else matters but hitting up the beach with the fam!!!

James Hetfield took his son and daughter to the Greek island of Mykonos Wednesday for a fun-filled day in the sun and a dip in the sea ... a day that never comes for some ... so they made the most of it.

Hetfield managed to maintain a rock star look with his camo trunks and a cross necklace chain ... while also flaunting his tats.

The Metallica co-founder probably would have been unforgiven by his kids if they went to Greece and didn't explore the beautiful island -- sad but true -- but instead ... he's the hero of the day.

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