The most picturesque...

of medieval walled cities must be Visby, on Gotland, a large and unusual carbonate island in the western Baltic, administered by Sweden (click to enlarge):

Part of our group approaches the north gate in the 3.4 km long limestone block wall, constructed during the 12th century and complete with a moat, that surrounds most of the city and the old church ruins:

And here's a shot of the ornate exterior of the more contemporary Visby Cathedral.  I particularly like the carved figure on the left, courageously tackling a lion and forcing its mouth wide open:

This mural, consisting of a  mosaic of stone chips and fossil crinoid stems (look closely), caught my eye during my wanderings of the streets in town during a personal early afternoon exploration:

Later, aboard ship, I presented my final lecture of the voyage on the plate tectonic assembling of northern Europe, starting with Baltica, an early-Paleozoic continental mass.