Great article appeared in our city newspaper and the information on the Rick Steve's web pages is also very good. However, one idea was missing: use a Google Fi cellphone.
Two options here: 1) purchase and full up Google Fi cell phone or 2) obtain a free SIM card free from Google Fi and use it in your personal cell phone. There are advantages to using the full-up Google Fi cell phone for phone calls, data and text messaging.
I purchased a Google Fi Motorola phone 2 years ago prior to a trip to Europe. It was incredibly easy to use in Europe--in Germany, Austria and Hungary (although in Hungary I used an app developed for Google Fi to assist network provider selections). Previously I had used Verizon and for one trip even used a T-Mobile SIM card but it was a lot more costly overall and more difficult to use. A friend of mine and his wife have traveled extensively around Central and Eastern Europe in recent years and have reported widespread success with their Google Fi phone.
Oh by the way, the Google Fi also works without extra charge, based on my personal experience, in Puerto Rico, Canada, and Costa Rica; and, basically most other places.
Normally, I try to limit most of my use to WiFi, but what a useful tool to have data access. For example, on my last rip to Europe a river boat ferry was not running due to low water levels. Using local German transit apps I was able to identify a bus to route us to our destination and back. And, back home in the USA, I pay half of what my wife pays for her Verizon account.