Because the tour books are all organised by country, we tend to think in terms of 'An Italian holiday' or 'a tour in France'...
But we might be missing a trick. Country borders weren't set in stone within Europe until the late 19th century. And airports aren't always sited neatly for country borders.
For instance, depending on where you want to go in Slovenia, it might be better to fly into Graz (Austria) or Trieste (Italy) than Ljubljana airport.
The Venetian empire did cover most of North-East Italy at one point. But equally, it covered the Adriatic coast of Slovenia and Dalmatia - cities like Koper and Piran show strong Venetian influences. Equally, Robert Adam's tour of Dalmatia in the 18th century showed how Spalato (as it was then - Split today) could be seen as part of the Roman Empire, rather than a hinterland of Slavic culture. Perhaps heading east from Venice down the Slovenian and Croatian coast could make an interesting holiday.