noun
optional tour
A supplementary excursion offered alongside a main travel package, typically at an extra cost.
このツアーでは、自由時間にオプショナルツアーに参加できます。
On this tour, you can join an optional tour during your free time.
オプショナルツアーの申し込みは、出発の3
Please book the optional tour at least three days before departure.