Step inside Casino Marino, however, and the arithmetic stops making sense. What appears externally to be a modest garden retreat conceals sixteen finely decorated rooms arranged across three floors, a spatial illusion so complete that visitors have been wrongfooting themselves for the better part of two and a half centuries. The name itself compounds the joke: "casino" is simply Italian for "small house."

The building was designed by Sir William Chambers, one of the leading architects of the eighteenth century, as a pleasure house for James Caulfield, the 1st Earl of Charlemont. Caulfield was a well-travelled Anglo-Irish nobleman with serious architectural ambitions, and Chambers gave those ambitions full expression here. The result is considered one of the finest neo-classical buildings of its era in Europe, a category that takes in a great deal of accomplished stonework across a very large continent. Neo-classicism, broadly speaking, drew on the forms of ancient Greece and Rome, prioritising symmetry, proportion, and restrained ornament, and at Casino Marino those principles are applied with exceptional precision. Every external detail has been calculated to deceive the eye about the building's true scale and internal complexity.

The Casino sits at Marino, just off the Malahide Road on the northside of Dublin, close enough to the city to reach easily but tucked away enough that many Dubliners have never quite got around to visiting. The building is managed as a heritage site and is open to the public, with guided tours available that are genuinely worth taking, since much of what makes the interior extraordinary is easy to miss without someone pointing it out. The decorative detailing in the rooms rewards close attention, and the engineering ingenuities used to hide functional elements within the classical facade are the kind of thing that becomes more impressive the longer you look.