I was on a trip from Belgium to Spain and decided to have a little stop over in Paris to see some of the sights. One of the main sites that I knew I would have to see was the Notre Dame Cathedral (Cathedrale de Notre Dame de Paris)
The cathedral started to be built in 1163 and finished almost 200 years later in 1345. My guide book from the hotel had great information, as I walked around the cathedral I read how the building was badly damaged and falling into disrepair after the Revolution, but luckily renovations were made to the gorgeous cathedral.
I walked around reading the history, to go inside it was free, but if you want to go to the top to see the Montmartre to the north, the Arc de Triomphe to the west and St-Sulpice and the Pantheon to the south youll have to pay a small fee. I opted out of this and enjoyed the sites individually. You can also go to crypt for around $5 USD.