The Cathedral is truly beautiful, if you enjoyed the Vatican city then you will like this place. This is a UNESCO World Heritage Site. There is no photography inside, and there are lots of stern looking ladies sitting inside that will stare at you in you get your phone out. There are also a few beautiful artifacts, such as the image of Mary made from painted Easter Eggs. There is a scale model of ancient Kyiv with a free speaker in multiple European languages that last about seven minutes. There were tours available but only in Ukrainian/Russian on an adhoc basis.
The Bell Tower provides views across the city. Watch out for the metal post about ten steps up. You quickly realise that you need to duck to avoid it. The steps are not crazy small, and they are broken up by the viewing platforms. The tower in Princes Street in Edinburgh is much tighter and busier than when I went in late December, but until you get to the first viewing platform the steps do get quiet small. A combined ticket was 200, roughly 6 euros in Dec 2018.