Caravaggio, the Baroque master with a penchant for violence and violent imagery, died young and left only 65 works to amaze. Now there are 66. The new painting, lost since the 17th century, was found in an attic in 2014, and is expected to fetch $170 million at auction in June.
Found in an attic? What sort of home has a 400-year-old masterpiece in the attic?  The painting is of Biblical Judith beheading Holofernes (bloodletting being a favorite theme of Carvaggio). I embed only the fair Judith's face; this NYT assessment shows the whole.

Leonardo da Vinci is another master whose every precious painting or drawing is prized, so "lost" works seem to come up frequently. Last year it was the $450 million Salvatore Mundi.
In 2019,  it's a charcoal sketch of a nude woman known as the Monna Vanna. 
The sketch wasn't really lost, but is in the news now because experts just realized how closely it resembles the Mona Lisa. (Do you find that hard to believe? Me too.) For years, they didn't think Leonardo drew it; they were put off by some right-handed cross-hatch marks, knowing Leonardo was left-handed. New research shows that the bulk of the sketch was done by a left-handed artist.
This piece hints at a possible male model for the sketch.

Finally, we ask: How can a painting 10 by 20 feet get lost for centuries? Found behind a 19th century wall in a Paris building, the painting dates from 1674 and depicts the entry of King Louis XIV's ambassador into Jerusalem. 
The building was being renovated for a new Oscar de la Renta Boutique when the painting was found. An agreement has been reached according to this very detailed and entertaining article from the NYT: the Boutique's lessees will pay to restore the painting, and it will remain in their store for the life of the lease.