When do you pay in advance for the Etna excursion?

When do you pay in advance for the Etna excursion?

  In order to make the reservation correctly, the Coop. of the Etna Nord Volcanological Guides undertakes to withhold 50% of the total cost of the service, which can be reimbursed only in case of cancellation by the guide company for reasons of force majeure: bad...