Heritage Open Day: Ever wondered what the old St Katherine's church's story is and what it is now when passing its majestic exterior at the foot of Lincoln's High Street? Come on in and find out! Founder of the medieval priory of St Katherine, on what is now the South Common, and one of the most influential figures in Lincoln’s history, St Gilbert (or Gilbert of Sempringham, as he was known before his Sainthood) is celebrated in the former church of St Katherine, now a Grassroots venue known as Southside.