St Catherine's, one of the oldest churches in Gdańsk, was founded in the late 12C, but its construction dates back to the 14C and 15C. This is where the tombstone of astronomer Jan Heweliusz (1611-1687) was identified in 1985 and also the site of his epitaph. Major artworks are housed inside. For the occasion of the 400th anniversary of the birth of Heweliusz in 2011, a pulsar clock was installed in the church. It is now the most accurate clock in the world.