Each participant will have to ascertain applicable visa requirements, and the conference organizers take no responsibility for it. We may be able to help by supplying e.g. invitation letters (which should not be needed in most cases, anyway). The following information is supplied purely as guideline and it is the participant’s responsibility to make his/her own visa arrangements.
Both the conference, and the field trips, are held in countries belonging to the “Schengen” space, the European common visa space. Therefore, a single “Schengen” visa (issued by any member state of the Schengen space) should allow you to travel in all countries and cover all activities related to the conference.
Citizens of many countries do not need a visa to come to Europe. If you need a visa, the most common type, known as the “Schengen visa“, allows travels up to 90 days to any member state, for tourism or business purposes, and should meet your needs. In any case it is the participant’s responsibility to check.
Note that since January 1st, 2021, the United Kingdom has left the Schengen space. You may need a different visa should you want to visit UK. For some nationalities, you may also need a transit visa should you change flights in a UK airport (check here).
We certainly hope that by September 2023 that crisis will be over, but you also want to ascertain if sanitary restrictions (Covid-19 vaccination, test, etc.) apply.