My experience worshipping at the high mass in the Köln cathedral differed from what I was used to, in terms of practices within the service as well as the landmark outside of it.
I grew up in a non-denominational community church, where services would include a few contemporary songs to open and close and a message in the middle from one of our pastors. While I have had experience in more denominational services that involve singing out of hymnbooks, I have never been to mass before.
Not counting the German that was mainly spoken, and the other significant difference of being a landmark, the first change that I experienced would be the incense that was spread at the start of the service. One of my friends explained the concept to me. The early days of the catholic church were during a time where people were not too clean. Combine this with the close quarters of churches and one would get a smelly combination. To encourage people to stay, there would be incense spread at the start, with the tradition continuing even after people became cleaner and churches larger. Another friend who is catholic also mentioned that the tradition of incense was done to also ward off spirits and cleanse the air.
Another difference would be the way the hymns are sung, which I actually liked in the service. Instead of everyone singing collectively for all parts, there are separate parts that the choir sings that are distinguished in the hymnbooks as well as by less involved organs. It seemed similar to a call and response, except done through song.
What I find most fascinating was not in service but out of it, with the cathedral being the tourist attraction that almost 20,000 people visit on each day. While the cathedral is another sight to behold, I find more interesting the way a place can be both an attraction and a functioning church. The aspects of a popular spot are present: guards check entrances, paid pamphlets to provide historical context, a souvenir shop exists, large crowds go about, etc. Despite this, the service itself, aside from a thank you and acknowledgment in English to the visitors from one of the congregation leaders, is untouched by these touristy aspects. One question that I do have would be how close-knit the local congregation is, given the number of people like myself who only visit on a trip.