The metropolitan cathedral of Buenos Aires is the main Catholic temple of Argentina. The hours for visits are from Monday to Friday from 8 am to 7 pm and Saturday and Sunday from 9 am to 7:30 pm. Guided visits are free. Check here for mass times. The cathedral is located at Plaza de Mayo.
Pacific Galleries is one of the most crowded malls in the city. This place was declared a historical monument and it was built in 1889. It's open from Monday to Sunday from 10 am to 9 pm and Sunday from midday to 9 pm. It's located at Florida street and Cordoba avenue. Check here for more details on what to do in Buenos Aires in Florida street.