Amposta Main Festival Activity · Amposta, Montsià, Tarragona Image of Amposta, not of the place itself. Amposta's Festa Major is held in the capital of the Montsià, whose Torre de Sant Joan, built in 1576 by order of Felipe II, now stands some fifty metres out to sea owing to changes in the coastline. Photo: Enric (CC BY-SA 4.0) What to see and do in Amposta