I am what people would term a dati tziyoni jew currently living in chu"l. Is it permissable for me to attend martial arts classes if they are held, once a week, in the hall of a church, and this is the only location that teaches this specific art? Presumably it is not the part where people pray but rather a function hall etc. and possibly it is not connected to the main church at all (i haven’t been there yet, hence my question, so i wouldnt know). Thank you.

It is forbidden to enter the sanctuary of a church, even when prayer is not conducted. Other rooms in the building may be entered if it is not during the time when prayer is being conducted in the sanctuary, if the entrance is not that which a churchgoer would normally use to enter the sanctuary, and if the purpose is not religious (for instance if a voting booth is in a church).