You either love it or you don’t care at all about Bloomsday, there seems to be nothing in between. It is a HUGE day for some and others don’t even know what it is about. If you belong to the latter group, let me help you a bit.
Bloomsday is a made up day and nothing of it is based on real events. James Joyce wrote the book Ulysses between 1914 and 1922 and the book describes one day, Thursday 16 June 1904 when Leopold Bloom, a fictional figure in the book, went about his business from 08:00 to the early hours of the next day. This invented day, lived by an invented person became Bloomsday.
You could compare it to McClane Day! Which doesn’t exist!!! But would be the day just before Christmas when we copy all the things that John McClane did in Die Hard. We go to Nakatomi Plaza for a Christmas Party, have a disagreement in the toilet and then spend the rest of the day to fight against Max Gruber and some terrorists/thieves with all sorts of weapons. So if McClane Day makes sense to you, then Bloomsday will also make sense.
The James Joyce fans dress up like characters from the book in clothes that were worn by people around 1904, then they have a breakfast like Leopold Bloom and visit the locations he went to during the day.
Does that help a bit? If not, get a better description here: en.wikipedia.org/wiki/Bloomsday :-)
I think we should plan for McClane Day! We just have about 6 months to prepare for it! :-O