Where: The Pergamon Museum, Berlin (Bodestrasse 3; +49 30 2 6642 4242).
Few pieces are great enough to have an entire museum named after them.
The Pergamon Museum in Berlin isn't exactly short of massive ancient monuments either -- but the Pergamon Altar trumps the rest.
Transported from modern day Turkey, this monumental stone altar dating back to the 2nd century BC cows visitors with its size, then draws them in with astonishingly detailed friezes depicting the battles between gods and giants.
What: Théodore Géricault's "The Raft of the Medusa."
Where: The Louvre, Paris (4 Place du Louvre; +33 01 40 20 53 17).
Courtney Obee Delaunay, art historian and docent for Context Travel, goes beyond the "Mona Lisa" to pick Géricault's monumental marriage of high art and journalistic sensationalism.
"The dramatic scene vividly depicts the makeshift raft holding the emaciated and even corpse-like survivors of French shipwreck The Medusa, abandoned by its politically appointed captain," she says.
"Géricault represents the figures in a very realistic, yet also heroically classical way. It creates the perfect bridge between earlier masterworks found in the Louvre and the early modern works on display at the Musée d'Orsay."
What: "The Saliera."
Where: Kunsthistorisches Museum, Vienna (Burgring 5; +43 1 525 240).
The Kunsthistorisches Museum is home to masterpieces by the likes of Vermeer, Rembrandt, Raphael and Caravaggio but Sabine Haag, the museum's director-general, points to Benvenuto's "Saliera" as the must-see.
"A unique work of goldsmith art, the complex pictorial program culminates in an allegory of the cosmos with the god of the sea and the goddess of the Earth, animals, the four winds and the four times of the day," says Haag of the piece returned to the museum this year after another decade-long renovation.
"'The Saliera' is a truly virtuoso piece -- we know from Cellini's autobiography that he hammered the figures from gold foil with every refinement he could imagine."
What: Picasso's "Guernica."
Where: Museo Nacional Centro de Arte Reina Sofía, Madrid (Calle de Santa Isabel, 52; +34 917 74 10 00).
Four of the 15 most expensive paintings ever sold are by Picasso, yet the work widely regarded as his greatest masterpiece would almost certainly smash all records if put up for auction.
Guernica's size -- 3.5 meters by 7.8 meters -- makes it unusual, but it's the political commentary about Nazi bombing during the Spanish Civil War and the layers of symbolism piled within that make it arguably the most famous artwork of the 20th century.
What: The Parthenon sculptures.
Where: The Acropolis Museum, Athens (15 Dionysiou Areopagitou Street, +30 21 0900 0900)
There's no greater symbol of Ancient Greek classicism than the Parthenon, and most of the treasures from Athens's hilltop temple are inside the Acropolis Museum.
Dr Tom Flynn, author of "The Universal Museum," says the Parthenon sculptures are the pinnacle of Greek high classical sculpture.
"Their location in the Parthenon Gallery of the New Acropolis Museums allows us to appreciate them in the context of the Parthenon itself. You can faithfully recreate their original disposition on the temple, which is visible from the gallery," he says.
What: Mantegna's "Dead Christ."
Where: Pinacoteca di Brera, Milan (Via Brera 28; 00 39 02 722 631).