The Middle Ages
Trails
Cathedrals
There's about a million pictures of cathedrals, so I've picked only a couple more or less at random. This one is one of the more famous: the cathedral at Chartres. Find out more about this one and read about Abbot Suger, too.
When you are looking around, see if you can find out what the word means. In Latin, it is cathedra.
This one is in Caen, but there are many others. There's a great web site for the cathedral of Amiens that is well worth visiting.
Take the time to visit more than just French sites. English and German cathedrals are easy enough to find (what is the German word for cathedral? What's that word mean?), but look for Italian and Spanish ones as well (same question about language).
Then go further afield. Look for Polish cathedrals--not just a church mind you, but a cathedral--or Danish or Hungarian. Is there such a thing as a Russian cathedral? Why or why not?
Even though this isn't medieval, take a look at modern cathedrals. There are some excellent ones in the United States.
Finally, and this is just for my Boise, Idaho students: go visit the Cathedral of the Rockies. Is it a cathedral?