Two blocks south of Iglesia Parroquial del Espíritu Santo [1] is Nuestra Señora de la Merced (Our Lady of Mercy, Cuba #806, esq. Merced, tel. 07/863-8873, daily 8 a.m.–noon and 3–6 p.m.), a small handsome church and convent with an ornate interior containing romantic dome paintings and the Capilla de Lourdes (Lourdes Chapel), also with early-20th-century religious frescoes.
Iglesia y Convento de Nuestra Señora de la Merced, begun in 1755, has strong Afro-Cuban connections (the Virgin of Mercy is also Obatalá, goddess of earth and purity), and it is not unusual to see devotees of santería kneeling in prayer. Each September 24, scores of worshippers cram in for the Virgen de la Merced’s feast day. More modest celebrations are held on the 24th of every other month.
Links:
[1] http://www.moon.com/destinations/cuba/havana/sights-habana-vieja/southern-habana-vieja/iglesia-parroquial-del-espiritu-santo