We went to see Notre Dame around noon and only had to wait roughly 15 minutes as the queue moves very quickly. It was a huge benefit to have a professional guide explain the history, artwork, paintings, etc as it gave us a real appreciation of the spectacular beauty of this cathedral. There is no admittance fee but you are able to provide a small donation to light a candle on behalf of needed prayers or a loved one. The stained glass rose windows are breathtaking. I clearly felt I was in the presence of God throughout.