The dominant feature of the interior of the basilica is the 24-metre high main altar, whose sculptural and woodcarving decoration was created by A. Dorasil and his workshop, according to a design by F. Brokoff.
The altarpiece, decorated with statues of nine angelic choirs, recalls the verses „Exaltata es sancta Dei Genitrix super choros Angelorum ad caelestia regna” [Exalted are you, Holy Mother of God, above all the angelic choirs to the heavenly kingdom].
In the centre of the altarpiece is a painting by the Czech Rubensian Peter Jan Brandl, depicting the Assumption of the Blessed Virgin Mary as she rises vertically to meet her Bridegroom, who awaits her together with the Father and the Holy Spirit. At the empty tomb, the apostles have gathered, some of whom are gazing at the tomb and some of whom have already noticed Mary walking towards the heavenly light. Beneath Brandl’s painting, a small icon of Our Lady of Grace is placed in an ornate frame. The miraculous image of the Mother of God is dated to the 13th century, making it the oldest icon in Poland and Central Europe.