Analysis of information sources in references of the Wikipedia article "Bloomsday" in English language version.
They walked to Ringsend, on the south bank of the Liffey, where (and here we can drop the Dante analogy) she put her hand inside his trousers and masturbated him. It was 16 June 1904, the day on which Joyce set "Ulysses". When people celebrate Bloomsday, that is what they are celebrating.