First time cruisers. I think we would enjoy exploring the cities on our own a bit, rather than packing each day with group excursions. (We look forward to meeting our fellow passengers, but also want some time on our own. And we prefer walking to motor coach/bus.) Are there particular stops that are better suited for this? In terms of access to a city center from the boat? Conversely, are there stops that we just need to bite the bullet and board the bus?