Medieval Cathedrals were a very holy place to people all around. First off the bishop of that cathedral held his headquarters there. The cathedral was very sacred to Christians because this is the only other place they could pray to God in peace. Also the Christians took communion here. Masses were held here as a place to show love and thanks towards God. There were pews for praying, you could sit or stand it didn't really matter. The architecture of the cathedrals came and were based on the cathedrals in ancient Rome. The cathedral was also a meeting place. If a king or noble or someone famous was in everybody would go to the cathedral to hear the important message being spread. Cathedrals were generally bigger than churches because they were built to hold more people for bigger services like mass. Building the cathedrals during the Middle Ages was a reflection of faith and a channel of creativity for most Europeans. Cathedrals were a place to to spend time with God and forgive sins.
This is a picture of stained glass inside a cathedral.