Never underestimate the value of those boxes gathering dust in your basement. The contents could be worth a cool few million.

A cardboard box full of hockey cards that sat in a basement in Saskatchewan, Canada for decades sold for $3.72 million, according to a press release issued by Heritage Auctions.

Inside the large box are 16 other boxes containing 48 packs of O-Pee-Chee hockey cards from 1979-1980, totaling about 10,752 "fresh off the factory floor" cards total. In this collection could be a rare find: Wayne Gretzky's rookie cards.

"We knew from the moment we heard this O-Pee-Chee case existed that it would get the attention of hockey card collectors worldwide," said Chris Ivy, director of sports auctions at Heritage, in a statement.

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Ultra-rare Wayne Gretzky rookie cards may be inside

Manufactured by the well-known O-Pee-Chee company, the '79-'80 release became one of the most famous of all time, as it contained Canadian hockey legend Wayne Gretzky's rookie debut card. It is believed roughly two dozen such rookie cards from Gretzky's first season with the Edmonton Oilers are likely contained within the set, which is the only unopened case of 1979-'80 OPC cards to have ever surfaced in the 21st century, according to Heritage Auctions.

Heritage Auction said the owner of the cards was once a "rabid" collector who had such a sizeable collection, his family lost track of what he owned. Recently, his son discovered the lot behind "stacks and stacks" of other items.

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"Remarkably, our consignor wasn't aware he owned this outrageous Holy Grail case until very recent accounting of a long-forgotten pile of boxes in his home in Saskatchewan, where deadstock cards from the late 1970s and early 1980s had been gathering dust since he had bought them directly from a wholesaler," Heritage Auction said.

"By any metric of evaluation, it's a thrilling miracle of survival, and one of the greatest trading card lots that Heritage has ever had the privilege to offer."

Other major sales were made at the Sunday Winter Platinum Night Sports Auction, including a high-grade 1952 Topps Mickey Mantle card that sold for $2.37 million. In total, the event resulted in $25.98 million in sales.