1. The Louvre
2. The Prado
3. The Rijksmuseum in Amsterdam
4. The Museum of the Penis in Reykjavik
5. The Museum of Beefcake in Milwaukee, Wisconsin
Actually it's the Grohmann Museum on the grounds of the Milwaukee School of Engineering, home to the world's largest collection of art about "Men at Work."
A sizeable percentage of those men at work are beefy, muscular, and shirtless.
(It opened in 2007, so I unfortunately never went when I was living in Racine.)
Start off with the Rooftop Sculpture Garden, for a dozen 9-foot tall statues and 6 smaller statues of men working in fields, heaving hammers, pitching molten metal with their shirts off.
Then go inside for dozens more statues of men working in foundries, artisan shops, mines, and farms, such as The Stempelsetzer (Timberman), by Paul Vogelsanger (top)
Plus hundreds of paintings of working men (and a few women), mostly by German, Flemish, and Dutch artists who obviously enjoyed the nude male form.
Such as In the Military Forge, by Jules Delauney (left).
It's open 9-5 weekdays and 12-6 Saturdays. When you're done, look for This Is It, on Wells Street a few blocks away. It was named the Best Gay Bar in Milwaukee.
See also: A Beefcake Tour of the Louvre.