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
May you require a letter for your visa application to attend the conference, please read the following. You first need to register on CVENT (see registration information here). Do not forget to click on “Yes” when asked “Do you require a Visa Support Letter”. You will then be asked to send an email to ACM in order to receive your invitation letter.
Nantes time zone is the Central European Time (GMT + 2 hours).
Voltage and sockets vary from country to country, therefore an adapter and a transformer may be necessary: the standard domestic electricity supply in France is single phase 220 volts, 50 Hz.
To check the measures implemented in France related to Covid-19, please check: https://www.interieur.gouv.fr/covid-19-international-travel