NHL Legend Bill Guerin -- Drops $500K on Backyard Hockey Rink

Retired Penguins star Bill Guerin is living every hockey players dream ... 'cause the guy just dropped HALF A MILLION DOLLARS on a full-size ice rink in his BACKYARD, TMZ Sports has learned.

The 2x-Stanley Cup winner -- who now oversees player development for the Penguins -- had the rink installed in the back of his new home in Sewickley, PA ... just a 25 min drive from the Penguins stadium.

We're told Guerin even ordered a personal ZAMBONI machine to keep the ice in tip top shape.

Also looks like there's a basketball net at the end of the rink ... so we're hoping Guerin's in the process of inventing some sort of hockey-basketball hybrid sport.

The real winners here -- every kid in that neighborhood.