Here's a particularly impressive one from the intersection of College Road and Gaol Walk, right at the heart of University College Cork. It's a real whopper; nearly 6ft tall, and proudly encroaching onto the pavement so that it forces students to dance around it on the dash between classes.
This one is more recent than those of previous postings; it's a GR, so it must have been installed between 1910 (when George V took the throne) and 1922 (following Irish independence when, naturally, they stopped installing "Royal Mail" boxes). UCC was founded -- as "Queen's College Cork" -- in 1845 by Queen Victoria (George V's granny). So one wonders how the first students and staff sent their letters home (or manuscripts to academic journals) before this box's installation. It was the Queen's College, but they had to wait for the King's postbox.