Virtual Tours of Greatest Architecture of the World
My oldest son is a professor of Art History at the University of Colorado. He is an expert in 11th and 12th centuries. If you are a lover of architecture, he recommends that you visit this link which is an on-going project with Columbia University:
http://www.mcah.columbia.edu/ha/index.html
Note that you must download free software from Apple. This procedure is explained on this webpage.
The virtual tours are from:
Ancient Architecture
Early Christian & Byzantine
Medieval Architecture
Renaissance
Baroque Architecture
19th Century Architecture
Islamic Architecture