It may be hard to imagine because the Vismarkt is currently one of the busiest locations in Groningen, but it is believed that during the Middle Ages the Drentse Aa was an inland harbour here, with a wooden church. In 1226, the church received its official name: Kerk van Onze Lieve Vrouwe ter A, currently Der Aa church. Today it is used as a location for receptions, concerts, symposia and exhibitions.
https://toerisme.groningen.nl/en/see-and-do/culture/kerken-en-torens