The Pieterskerk Leiden from 1121 is the oldest church in Leiden. It is named after the apostle Peter, the patron saint of the city. Jesus said to Saint Peter, ‘I will give you the keys to the Kingdom of Heaven’. Leiden is called ‘key city’ and keys are the city’s coat of arms.
Once the place where the American Pilgrim Fathers went for prayer.
It is a large church and many university professors are buried there. The most famous graves are those of the painter Jan Steen and the scientist Herman Boerhave.
The Hooglandse Kerk is also very worth seeing. It is a late Gothic cruciform basilica with an impressive interior. The church also functioned to provide the people of Leiden with water. The large roof of the church collected a lot of rainwater, which was stored in reservoirs.

https://www.visitleiden.nl/en/locations/2974987658/pieterskerk