The closest airport to Kathedral Notre-Dame is Luxembourg Airport, which is located in Luxembourg. If you plan on visiting or staying in this area, landing at Luxembourg Airport will be your best bet.
The best prices found on momondo for flights to Luxembourg are:
£9 per person with Ryanair
£17 per person with easyJet
£34 per person with TAP AIR PORTUGAL
Luxembourg has restricted the entry of all travelers who are not Luxembourg nationals, and their family members who are returning home. Nationals and residents of the European Union, Schengen Member States, and the Schengen Associated States, the United Kingdom, and their family members who are returning home may still enter the country, along with healthcare professionals, border workers, diplomats, humanitarian aid workers, military personnel, travelers in family emergencies, and travelers on their way to their home countries by land who have proof of their onward journey may still enter the country. Travel restrictions for non-EU citizens are expected to remain in place through at least June 15. If you are planning to travel to Luxembourg at this time, it is recommended that you stay up to date on current restrictions and follow proper safety measures while in public.