For all the television shows that set out to solve the world’s great mysteries, and the intrepid adventurers hunting for lost artifacts, some of the most famous treasures of history are still missing. These include one of the most dazzling rooms ever made, a giant yellow diamond, and the work of a renowned Greek poetess. Here are just a few of these enigmas.

1. THE AMBER ROOM

Designed in the 18th century by German sculptor Andreas Schlüter and Danish amber artist Gottfried Wolfram, and gifted to Russia in 1716, the Amber Room of Catherine Palace was the pride of the Saint Petersburg area. Lavishly decorated in jewels, gilding, and, of course, panels of amber, it was sometimes called the "Eighth Wonder of the World."

When the German army neared Saint Petersburg during World War II, the curators at Catherine Palace knew they had to hide this treasure. They tried to take it apart, but the dry amber crumbled in their hands; instead they hid it behind wallpaper. German soldiers found the Amber Room anyway, and broke it down into pieces that were packed in crates and shipped to Königsberg, then part of Germany (now part of Russia). For a time, the Amber Room was installed in the Königsberg castle museum. After that, its fate gets fuzzy. Some researchers believe it was destroyed in the bombardments of the war, while others think that it’s still hidden somewhere. Despite periodic claims of it being found—and verified remnants turning up in 1997—most of it remains missing. In 2003, a reconstruction of the Amber Room was unveiled near Saint Petersburg, so visitors can at least get a glimpse of its lost glory.

2. SAPPHO'S POEMS

Sir Lawrence Alma Tadema, Sappho and Alcaeus (1881)Hulton Archive/Getty Images

Ancient sources state that the Greek poet Sappho penned nine volumes of writing, but only a couple of full poems—and a few hundred lines on shreds of papyrus and potsherds—survive. Some contain just a handful of words, yet they hint at the passion in her work: "I desire/And I crave," one remnant reads. Many of these bits survive thanks to her popularity in antiquity, since her writing was frequently quoted in other sources.

There may be more of Sappho's work to discover. A late 19th- to early 20th-century excavation at a trash dump in Oxyrhynchus, Egypt, turned up valuable fragments of her poems. As recently as 2014, two works on papyrus fragments were identified by an Oxford papyrologist. With any luck, there may still be scattered remains of her poems to unearth in the detritus of the classical world.

3. THE FLORENTINE DIAMOND

According to legend, Charles the Bold—the Duke of Burgundy—carried this 132.27-carat yellow diamond into the 1477 Battle of Nancy as a talisman. The treasure did little to protect him, however, and he fell along with his gem. His mutilated corpse is said to have later been recovered from the battlefield, but the diamond was gone, supposedly picked up by a scavenger who sold it for two francs because he thought it was just glass.

However, in the 1920s the art historian Nello Tarchiani did archival research that revealed the diamond likely had no connection to the duke. The gemstone had originated in southern India, where it stayed until the Portuguese seized the area in the 1500s. Soon afterward, it made its way to Europe and into the hands of a series of illustrious owners, including Ferdinand de’ Medici, the Duke of Tuscany, in 1601. It was in the treasury of the Medicis in Florence that it got its name—the Florentine Diamond—and most likely its glistening, 126-facet double rose cut.

When Anna Maria Luisa de' Medici, the last of the Medici ruling family, died in 1743, the diamond didn't stay with the treasure trove she bequeathed to the Tuscan state. Instead, Francis Stephan of Lorraine (who later became the Grand Duke of Tuscany and Holy Roman Emperor) bought it for his wife, Empress Maria Teresa, herself at the end of the House of Habsburg line. For a time, the Florentine diamond became part of the crown jewels in Vienna. Then the Austro-Hungarian Empire collapsed after World War I, and the diamond, it’s believed, was carried into exile in Switzerland by its last emperor, Charles I.

But where is it now? There are many theories on its disappearance, including that it was sold by the exiled emperor, and perhaps cut into smaller gems for that purpose. Others posit that it was stolen and spirited to South America. With no trace of the diamond in years, its whereabouts remain a mystery.

4. FABERGÉ EGGS

Peter Macdiarmid/Getty Images

The legendary House of Fabergé was once the largest jeweler in Russia, employing 500 designers and craftsmen to transform everything from mantel clocks to cigarette cases into delicate and elaborate works of art. Their most famous achievement is the series of jewel-drenched Easter eggs they produced for Czars Alexander III and Nicholas II, which the Russian rulers gave as gifts to their wives and mothers. Each egg contained a surprise, from the Trans-Siberian Railway Egg (with a wind-up train made from gold and platinum) to the Bay Tree Egg (shaped like a tree, with a mechanical singing bird emerging from its branches). After the Russian Revolution overthrew the Romanov Dynasty—and the imperial family was executed—the new Soviet rulers seized the eggs. Lenin was interested in preserving such cultural heritage, but Stalin saw them as economic resources, and the eggs were sold off. Out of the 50 Imperial Eggs (as the eggs created for the czars are known), seven are missing.

Information on the lost eggs is sparse. There are few photographs—the only image we have of one of the eggs, the Cherub with Chariot Egg, is a reflection in the glass of a display case. Sometimes the surprises inside are detailed in records, and in other cases they remain a mystery. However, in 2012 a Midwest man who had bought what he thought was a fancy doodad for scrap gold happened to do an internet search on the name on the little clock inside: “Vacheron Constantin.” He discovered that his trinket, which he’d bought for $14,000, was one of the lost Imperial Eggs, worth $33 million.

5. CROWN JEWELS OF IRELAND

Lord Dudley, Grand Master of the Order of St. Patrick, wearing what's often called the Irish Crown JewelsNational Library of Australia, Wikimedia Commons // Public Domain

On July 6, 1907, regalia belonging to the Grand Master of the Order of St. Patrick—referred to as the "Crown Jewels of Ireland"—were discovered to be missing, the keys boldly left hanging in the safe’s lock. The pricey pieces, which included a diamond star and badge, had been presented to the order of knights in 1830. As added insult, five collars of Knight Members of the Order had also been spirited away.

Security was perhaps a bit lax. A safe room had been built for Dublin Castle in 1903, yet the safe that protected the jewels was too big to fit in the door, so it was kept in a library strongroom.

An investigation was immediately launched, but a century later, the case is unsolved. One rumor is that the investigation was halted under the orders of Edward VII because it ended up touching on a sexual scandal at Dublin Castle. One top suspect is Francis Shackleton, second-in-command at the castle, and brother to the famed explorer Ernest Shackleton; some say he may have been trying to raise funds for his brother's polar expedition.

6. ART FROM THE ISABELLA STEWART GARDNER MUSEUM

Empty frames at the Isabella Stewart Gardner MuseumFederal Bureau of Investigation, Wikimedia Commons // Public Domain

In the early morning of March 18, 1990, the security guards at the Isabella Stewart Gardner Museum in Boston buzzed in two men claiming to be police officers. Once inside, they handcuffed the guards and revealed their true intention: stealing art. They made off with 13 works valued at $500 million, the biggest unsolved art theft in the world.

Vermeer, Rembrandt, Degas, and Manet works are among the stolen art, although strangely, the robbers also opted to take a bronze eagle from the top of a Napoleonic flag and an ancient Chinese beaker rather than other, more valuable objects nearby. Because the museum’s collection and layout are permanent—both the legacy of the late art collector Isabella Stewart Gardner—the frames of the missing artworks are kept empty, a memorial and a reminder that the burglars are still at large. The FBI believes the paintings made their way to organized crime circles in Philadelphia, but haven’t had a lead since 2003. Currently, the reward is $10 million for information leading to the artworks’ recovery.

7. THE HONJŌ MASAMUNE

At the end of World War II, citizens in Japan were required to turn over privately owned weapons, including historic pieces. Among them was one of the most famous swords ever made: the Kamakura-period Honjō Masamune. Created by Masamune, who lived circa 1260-1340 and is often considered Japan’s greatest sword maker, the sword was celebrated for its strength and artistry.

Its last owner was Tokugawa Iemasa, who brought the Honjō Masamune, along with other heirloom swords, to a Tokyo police station in compliance with the Allied orders. They were handed off to someone in the Foreign Liquidations Commission of AFWESPAC (Army Forces, Western Pacific), then disappeared. Some surrendered swords from this era were brought back to the United States by American soldiers, while others were melted or tossed in the sea. Today, the fate of the Honjō Masamune is unknown.