You can’t go into a church because of avoda zora. The gemora says you shouldn’t even go into a *city* where avoda zora is practiced, but we can’t follow that since it is virtually impossible. But as far as a church, ALL the poskim say forbidden. (Mishna, Gemorah, Rambam, Ritba, Rosh, Rashba, Rav Moshe, Tzitz Eliezer, Rav Ovadia Yosef, et al).
I’m still waiting for one who says otherwise.
Anyone? There isn’t any.