Tell me about Rotterdam...

Rotterdam is a big, modern sea port with good rail connect. Because if its importance as sea port, the allies in WWII reduced it to a pile of rubble. Since nothing was left standing, it was decided to rebuild as a modern city instead of restoring it to what it was. It has some great modern architecture, good tram system, great bridges so it works well as city for day trips.

Rotterdam is very much praised for its modern architecture, but I can't be impressed.
Better stay in Dordrecht, a much overlooked city with an impressive history. Kinderdijk around the corner (take the river ferry, the Waterbus). Schiedam less than half an hour away. Even Gouda is just 45 mins. Both with trains running every 15 mins. Use this real-time planner for your public transport options: http://9292.nl/en#
A car is indeed totally useless.

Oh - I was leaning towards Rotterdam, but then looked at airbnb's in Dordrecht and there is a great one for $55 Canadian a night in a building that was built in 1680's! It has tons of good reviews (247) and the street looks totally charming that it is on. And it has a canal view out back from the balcony!! It may have swayed me back to Dordrecht!

Enjoy! Dordrecht is really a nice city, in fact the oldest in this part of the Netherlands.

the allies in WWII reduced it to a pile of rubble. Actually, that was Germany. The invasion of the Netherlands wasn't going quite as smoothly as planned, so they bombed Rotterdam into oblivion just to prove they could. A few years ago, there was a Dutch movie called "Het Bombardement" which depicted the assault (the film follows basically the same plot formula as Titannic, transposed to Rotterdam).

I spent two days in Rotterdam once. As you noted, it's mostly a modern city... if you exprapolate the post-war suburbs of other Dutch cities into a metropolis, you basically get Rotterdam. It won't win the award for most charming city in Europe, but it isn't ugly either. It has a rather large pedestrian shopping area as well, with a lot of bars and restaurants.

Dordrecht is another decent option. Imagine a traditionally cozy, but rather generic Dutch city without any real hightlights.

I'd also choose Dordrecht over Rotterdam. If North Americans want to see modern cities with cutting edge architecture, we can go to New York or Toronto or LA. When we go to Europe, we want to see something different. Because if the Nazi bombing, there isn't much left of the "old" in Rotterdam.

While Germany was responsible for the destruction of the city center, Allied bombing finished off the shipyards:

https://en.wikipedia.org/wiki/Allied_bombing_of_Rotterdam

So I was able to book the airbnb in Dordrecht. Since I like to get up early and go out to take photos, I think it'll be perfect and charming!

All train lines going to or through Rotterdam have at least half-hourly service from around 6.00 to 1.30 next morning.