I've made 5 River Cruise trips in Europe with Grand Circle Cruise Line. Prague and Budapest were included in these trips. The thing I've liked for the last three trips is the fact that two cameras and two lenses were adequate for this kind of travel. I shoot a Pentax K5 and a Pentax K5II and carry a Sigma 18-250 on one and a Tamron 18-200 on the other. So far I've never needed to go for the back-up camera but I carry it on the trips so I have it if needed. My primary lens has been the Sigma on the K5II. The cameras and some cleaning equipment is a relatively light load and I can pack two days of clothing and shaving gear in the backpack. This works for me, not necessarily any one else. I've been able to catch dancing, evening shots, night shots on the Danube, indoor events, inside cathedrals, and just about anything I was interested in at the time. A lot of the purpose of my trips has been to learn more about the people and places of Europe. By photographing the people and places and putting the photos in a family travel journal, the memories of each trip continue to be sharp in my mind. If the photograph is the main purpose of the trip, then my equipment list probably won't work.
Enjoy your trip. You will be well rewarded with memories.
I tried using my cell phone for photos. It is faster to use your DSLR set on automatic, you will have a sharper photo and your issue of composition with the sun on your phone viewer is gone. You have your DSLR with you and when you have the time make the settings you want.
Use it. I dropped my camera (Pentax) when stumbling on sharp rocks. I was bloody and the camera was scratched-it flew out of my hands in the fall. It's been about four years now and the camera & lens have been in use without any problems.
From the definitions above, I would suggest take the same photo with a wide open aperture and with a very tight aperture. Or, maybe take several sets of different subjects. Then compare the differences. Just thinking.
I have used a Sigma 18-250 for several years now. It only has one lock position and tends to creep when unlocked and pointed much over level (either pointed up or down). On the plus side-it is one tough lens. I took a fall in rocks and the camera went flying. I thought I had lost my camera and lens. Well the truth is, neither the camera (Pentax K5) or the lens were damaged. They are still a team and in use quite often.
I am a Pentax user currently using a Pentax K5II. I have some experience with photography but am certainly not a pro.