I’m going to an Orthodox church in a few weeks, just for fun and curiosity. Does that count towards my Sunday obligation?
No, not if there is a Catholic Church in your vicinity. If there is, you are not allowed to receive Holy Communion at the Orthodox Church either.
Catholics may receive the sacraments in Orthodox churches only in areas where there are no Catholic Churches (as in most of Russia).
Fr. Vincent Serpa, O.P.