The Valle del Bove on Mount Etna, with the current lava flows steaming at the summit (upper left of the photo; click to see it larger!)
A cinder cone (maybe two?) on Etna's south flank that was active during the 2001 eruption, with a channelized a'a lava flow at its base.
A Norman castle in the town of Aci Castello, Sicily. (This was a coolness overload for me; not only is it an 11th century castle, which makes the archaeologist in me drool, it's built on pillow lavas. How's that for geoarchaeology?)
Hydromagmatic deposits and dune structures on the island of Procida, just outside the Bay of Naples. These were chock-full of accretionary lapilli (which unfortunately disintegrated on the trip home).
The neatest spot on Procida, even if there was a lot of trash around - an angular contact between hydromagmatic deposits and the welded layer underlying fines-depleted breccias. The breccias were amazing - huge chunks of pumice, trachytes, obsidian, scoria, all packed together with almost no matrix, and grading into a "typical" ignimbrite. (Volcanologists don't understand a lot about how these are emplaced, but one of the PhD students in my department is working on it for her dissertation.)
The summit crater at Vesuvius, minus the dozen or so souvenir stands.
The Roman city of Hercolano (Herculanium), with Vesuvius in the background. We were lucky that there was almost no one visiting, unlike Pompeii (which I'll have to see another time). It was beastly hot, though.
A street in Herculaneum. You can actually still see all the charred roof beams and window frames - it's almost a little creepy, when you realize that people not only lived here, they died here.
Part of a map painted by Ignazio Danti in the Vatican Museum, showing the Aeolian islands from a 16th-century point of view. Looks like Vulcano and "Strongoli" were both active at the time!
And one of my favorite discoveries on the whole trip...the Pope's rock hammer. He's a closet geologist!*
*Okay, so it was a commemorative builder's hammer from the construction of some ostentatious overly-decorated edifice somewhere. I bet it would make a pretty decent fossil chipper, too.