St. Stanislas Dominican Basilica is one of Lublin's oldest churches, traditionally dated to the mid-13th century. After a major fire in the 16th century it was rebuilt in the Lublin Renaissance style, leaving it with a layered interior of chapels, vaulting, and devotional art.
It is close to the Old Town and easy to include while walking between Grodzka Gate and Lublin Castle. Go inside for the chapels rather than the facade; the richness is mostly within.