How can a Jew attend a Christian church service? Especially the church sanctuary. For an avodah zora service. It is strictly prohibited to enter. According to all poskim from the mishna and gemorah Avoda Zora to S”A (and Rambam, Ritba, Rosh, Rashba, etc.) to contemporary poskim (Rav Moshe, Tzitz Eliezer, Rav Ovadia Yosef, etc.)
The Rashba says even for pikuach nefesh you can’t enter.