There are still a few number of colonial churches left in Northern Samar. So you could go on a visita iglesia around the province.
On top of the list is the fortress church of Capul Island. The Capul Church is dedicated to San Ignacio de Loyola. It was built by the Jesuits by the 18th century and renovated by the Franciscans in the late 19th century. For more information, on how to get to Capul Island, read Capul Island's lighthouse and old fortress church.
Visiting the rest of the churches is very straightforward. Most of the churches only have their exteriors relatively intact. You can begin at the Bobon Church (dedicated to the Sto. Nino) and then proceed to the Catarman Cathedral. Nothing much is left of the original church except the main retablo.
Next on the list is the Pambujan Church. In the next town is the Catubig Church which probably has the most interesting facade and exterior among all Northern Samar churches. The last stop should be the Laoang Church. But since we visited Pinipisakan Falls in Las Navas, the sun had already set before we made that ferry crossing from Rawis to Laoang.