Nantes is a city that is easy to get to, by air, rail, and road. Nantes is indeed served by its airport, by high-speed trains, and is situated at the intersection of several highways.
Useful information on how to arrive to Nantes can be found here: https://lacite-nantes.com/pro/information/how-to-come-to-nantes-474088.html
To check the measures implemented in France related to Covid-19, please check: https://www.interieur.gouv.fr/covid-19-international-travel
Please email the firstname.lastname@example.org if you require a letter for your visa application to attend the conference. When requesting an invitation letter, please indicate your paper title.