For romance, City Walls at Sunset delivers.
The single most romantic way to do the walls — cooler than midday, softer light, and the crowds thinning as cruise passengers head back to ship. The honest catch is it's the same €40 ticket and a gamble against closing time (you must finish before they lock up); the very last entry can still be busy, and cut it too fine and you're rushed. When it works, it's unforgettable.