The Chiesa Madre, dedicated to San Leone Magno (Pope Leo the Great), is the parish church of Castellana and the principal building of the centro storico. The current eighteenth-century church replaced an earlier medieval foundation; the facade is a plain Pugliese baroque, but the interior is more elaborate, with a barrel-vaulted nave, side altars, and a small treasury of liturgical silver.
The most venerated object is a wooden statue of the Madonna della Vetrana, paraded through the streets each January at the feast of Sant'Antonio Abate. The church is usually open in the morning and again from late afternoon.