The school took us on a three days excursion to Goa.

Trip : a journey or excursion, especially for pleasure.
Picnic : an occasion when a packed meal is eaten outdoors, especially during an outing to the countryside.
Visit : go to see and spend time with (someone) socially.
Tournament : (in a sport or game) a series of contests between a number of competitors, competing for an overall prize.
Excursion : a short journey or trip, especially one taken as a leisure activity.

Synonym of Excursion is Trip