Steve Wilkin was looking through a boarded-up projection booth in the Long Island theater where he worked as a teen in the early 1970s when he discovered a six-foot-tall poster for the 1931 movie Frankenstein.

The film, based on Mary Shelley’s 1818 book of the same name, catapulted Boris Karloff to stardom, spawned several sequels and helped launch the Universal Classic Monsters movie series.

In 2015, the poster sold for $358,500 through Heritage Auctions, an auction house in Dallas, Texas.

In 1989, a man got more than he bargained for at a flea market in Adamstown, Pennsylvania when he bought a framed painting for $4. He found a document folded up behind the painting, which experts later identified as a rare first printing of the Declaration of Independence. The document is one of about 200 copies the printer John Dunlap made after the declaration’s ratification on July 4, 1776. The ink was still wet on this copy when it was printed, an auction expert told The New York Times, evidenced by the first line of the Declaration’s text appearing in reverse at the bottom of the page.

In 2000, TV producer Norman Lear bought the copy discovered at the flea market for a record $8.14 million through Sotheby’s, a global auction house.

While fishing in Northern Ireland’s Arney River in 1965, Ambrose Owens discovered an unusual object. He left it in an old barn on his family farm in County Fermanagh, where it sat for more than 50 years until his brother Maurice passed it along to archaeological experts. Maurice was shocked to learn that the object was a Bronze Age sword dating back some 2,600 years.

In 2016, BBC News reported that Enniskillen Castle Museums in County Fermanagh planned to take over maintenance of the sword.

In 2006, a man in England found an old violin in his attic that turned out to be the one Titanic bandleader Wallace Hartley played as the ship sank in 1912. Shortly after the disaster, recovery workers found the violin in its case strapped to Hartley’s body at the site of the wreck. (Like many of the people who died that night, he was wearing a life preserver that kept his corpse floating in the water.)

Recovery workers sent his body and violin to his fiancé, Maria Robinson, in England. After her death, it passed through several other hands before landing with the mother of the man who found the violin in his attic.

In 2013, the violin sold for around $1.7 million through Henry Aldridge & Son Ltd, an auction house in Devizes, England, a record for a Titanic artifact. It has since gone on display at the Titanic Museum Attractions in Branson, Missouri and Pigeon Forge, Tennessee.

In 2004, a scrap metal dealer found a gold, jewel-encrusted egg at a flea market in the U.S. Midwest. He bought the egg, which opened up into a clock, for $13,302, hoping to melt it down and resell it for more. Upon researching it, he began to suspect that it was one of the lost eggs made by the House of Fabergé for the Russian royal family—objects revered as pinnacles of design and craftsmanship and valued in the tens of millions of dollars. Experts confirmed that his flea market find was indeed the Third Imperial Fabergé Egg that Russian Tsar Alexander III gave to his wife, Maria Fyodorovna, for Easter in 1887.

In 2014, the egg was sold privately through a London auctioneer for an undisclosed sum.

The 60 classic cars—most of which started out as unique, luxurious, handcrafted beauties—had languished in the elements for decades. Some had been overtaken by vines and weeds, and most were turning into rustbuckets. Discovered on a farm in western France, they were originally owned by French entrepreneur and car enthusiast Roger Baillon, who began collecting them in the 1950s, and whose plan for an open-air car museum was foiled in the 1970s by his failing finances. When Baillon's grandchildren inherited the farm, they discovered the decaying trove.

Among the cars in better condition was a rare 1961 Ferrari 250 GT SWB California Spyder, one of only about a dozen of this particular model made by the renowned sports car maker. It had once belonged to French actor Alain Delon, boosting its provenance.

In 2015, the car sold for $18.5 million through Artcurial, an auction house in Paris.

While cleaning out his aunt’s attic in Defiance, Ohio, Karl Kissner was surprised to discover more than 700 baseball cards dating from around 1910. The nearly pristine cards, part of an extremely rare series that had originally been given out with candy, featured Hall of Famers like Cy Young, Honus Wagner and Connie Mack.

In 2012, Kissner’s family sold the first batch of 37 cards for $566,132 through Heritage Auctions.

Michael Rorrer was cleaning out his great-aunt’s home in Virginia when he discovered 345 comic books stacked in the basement closet. He later learned that his great-uncle had compiled the collection, which included the first appearances of Superman and Batman, as well as the first issue in the Batman series.

In 2012, a large portion of these comics sold for $3.5 million through Heritage Auctions. The top seller was a 1939 copy of Detective Comics No. 27, the first comic in which Batman appeared, which went for about $523,000. A 1938 issue of Action Comics No. 1, the first comic in which Superman appeared, sold for roughly $299,000; and a 1940 issue of Batman No. 1 sold for about $275,000.