The Sieniawski Chapel in Brzeżany is one of the largest family mausoleums in the former Republic. The castle church dates from around 1554, with the Sieniawski family chapel being added to it in the years 1619-1624. The mausoleum gained a rich interior, decorated with mosaics, frescoes and precious materials such as marble. Only four tin sarcophagi from the 17th century by Jan Pfister, now stored in Pieskowa Skała, have survived to this day from the interior furnishings. The Polonica Institute has been working on the Sieniawski Chapel since 2020.