Training: get use to walking more, especially on cobblestone terrain. Walking on anture trails help with the training and walking on UNEVEN ground. You can't jus go out and walk for a whole day without walking on a regular basis.

Footware: Good shoes, have them broken in. I have ECCO Biom. Hiking boots is overkill for European city terrain and it is additional weight.
If you have odd shaped feet getting the shoe fitted is a good idea (not cheap but they might be covered under medical benefits)

Socks: Compression support socks is a must for calf muscles.

Post walk footcare: Epson salt soak, calf massage.

My DW and another couple did a 18 days Med. cruise. It was one sea day followed by one or two port days. Since we can relax on the sea day we took train into the city and walked around to see all the sights as time permitted. Snack, cafe and gelato breaks helped.