In no particular order:

Pompeii, Italy. Explore the ruins of this famous Italian city.

Colonial Williamsburg. Get a street overview of colonial Williamsburg, then click on certain features to learn more about each of them.

Vatican. Take a tour of the grounds and the cathedral at the Vatican.

US Capitol Virtual Tour. Tour the United States Capitol building here.

Supreme Court Tour. Select a room, including select justices’ chambers, and get a 360 view of each.

Stonehenge. Google Maps presents this virtual tour of Stonehenge.

Berlin. Visit some of the magnificent churches in Berlin, but don’t forget to see the Berlin Wall, too.

Palace of Versailles. Go to France with Google Maps to take a tour of this famous French palace.

Pisa. Look from the top as well as take a peek inside this famous leaning tower.

Mount Vernon Virtual Mansion Tour. View the estates and gardens of George Washington on this tour.

Cathedrals 3D Tour. View famous cathedrals all over the world.

Castles and Palaces 3D Tour. Take a look at the stunning beauty of castles and palaces around the world.

National Registry of History Places. Take a look at the historic places included on the National Registry.

United States Capitol Buildings. How else could you tour all the capitol buildings in one day?

Rome Colosseum. If Rome is too far off your travel map, visit virtually to see the famed Colosseum.

(Thanks onlineuniversities!)