When an occasion is extremely formal and full of rituals, you can call it ceremonial. Your cousin's fancy wedding and your friend's bar mitzvah are both ceremonial events.
The ritual of a new queen being crowned is ceremonial, with its pomp and formality. The way your family celebrates Thanksgiving might feel ceremonial to you as well, if everyone takes it very seriously and sticks to firm rules about what food to eat and who carves the turkey. Ceremonial originally described a purely religious ritual, from the Latin caerimonia, "holiness or sacredness."