From Ammoudi Port Santorini, to Riva Port on Therasia island  Santa Irini Retreat 
7-10min. (By boat)

From Athinios Port  Santorini at 15:30,  to Riva Port on Therasia island Santa Irini Retreat , arriving at  16:20,  (Sunday N/A). Best option if you arrive to Santorini by boat or if you have a car

By helicopter from Santorini
15-20 min.