I think it would be enjoyable/instructive for us to think about these. No ranking-#1 is not necessarily better than #30. We are limited to the number of European trips we have made. Those who have been on countless trips are limited to a maximum of 30. The major cities cannot be listed as a sight, but smaller places, like Fussen(which would make my second tier) are ok. For less familiar sights, please list town and country.
My list-I've been to Europe 16 times
Westminster Abbey
St. Fagan's Museum of Welsh Life
Sainte Chappelle(Paris) EDITED: you can go to a concert here and if you do it in late afternoon, the stained glass is amazing!
Sistine Chapel
Museo San Marco-because it's a rare opportunity to see the art in its original location-Florence
Pompeii
Parthenon
Troy
Ephesus
Hermitage Museum in St. Petersburg
Pergamon Altar, Berling
Ypres, Belgium- I didn't realize what a big deal WWI was in Europe until I went to Ypres
Anne Frank House
Mt. Pilatus-my only visit to Switzerland
Florence Duomo
Eagle Pub in Cambridge, where structure of DNA was first unveiled