Ir à igreja
This is a literal translation of the phrase, meaning "to go to the church."
Here are some other ways to say it, depending on the context:
* Frequentar a igreja (to attend church regularly)
* Visitar a igreja (to visit the church)
* Fazer uma visita à igreja (to make a visit to the church)
The best way to say it depends on the specific situation and the level of formality you need.