A limited-edition solid gold Lego piece has been auctioned off 20 years after it was first released—to the tune of almost $20,000.

The piece, a 14-karat gold Bionicle Hau mask, was discovered in a box of jewelry donated to a Goodwill store in western Pennsylvania. Bionicles were a divisive line of action figures Lego released in the early 2000s in an attempt to draw in new audiences and deviate from the traditional bricks Lego is known for.

The toy company used to run competitions with the grand prize being a fully playable gold karat edition of a Bionicle mask. It’s estimated that around 30 masks were made available in 2001, with 25 circulated as competition prizes and the remaining masks claimed by Lego employees. It was an unexpected discovery, then, for workers at the branch of Goodwill in Dubois, Pennsylvania, when they found the piece among a grab bag of jewelry.

But workers at the Goodwill store had no clue as to the item’s value. “No one thought anything of it,” Chad Smith, the head of e-commerce at the Dubois store, told USA Today.

The 14K Gold Lego Bionicle Hau mask. Photo: ShopGoodwill.

The staff listed the item on their retail platform, ShopGoodwill, when they were suddenly inundated with offers. “We didn’t know it was worth anything until people started asking if they could buy it for $1,000,” said Smith.

The piece was auctioned off in February. It was initially won by a bid of $33,000 but the buyer failed to cough up the money, so it was re-listed. After another round of 48 bids, it sold for $18,101, making it one of the most expensive individual Lego pieces ever sold.

In the world of Lego collectibles, a red Darth Vader helmet previously sold for almost $3,000, while a set of Boba Fett’s legs fetched around $1,000. “It’s the highest [priced] piece I’ve ever sold,” said Smith.

Smith added that the money from the auction will go toward supporting Goodwill’s mission of helping people with life challenges and providing training opportunities.