From NYC to Barcelona to London to Paris and Copenhagen, we have taken the Big Red Bus Tours where you hop on and off all day at your convenience. It’s best to take them (and they are everywhere the least bit touristy) for the full ride first and then pick and choose where you want to explore a bit, disembarking the Red Bus and then stepping back aboard at your leisure when you have had enough. This is one of the ways we traveled with the kids. They hand you earphones and you pick the language you want to hear as the narrator explains the sites you are zooming by. It is a quick overview.
In Barcelona, my family had had enough day tripping and stayed on to go back to the hotel and I stopped off and visited the famous Gaudi sculpture gardens and church. In Paris, it was a great way to get around and stop off at the Eiffel Tower, which was in a too far arrondissement for us to walk to. In London, we saw all the historic buildings and decided to get off at London Bridge and then walk around. In Copenhagen, where we just had a few hours on our cruise of the Baltics, we got to stop off at our first Ice Bar and the Viking Museum. In New York City, we passed by St. Patricks Cathedral and Ground Zero, finally descending at Battery Park so we could eye the Statue of Liberty.
I fondly remember those trips and how much fun we had and getting stuck upstairs (did I mention they are all double deckers)? where it is roofless and getting soaked during rainy weather and getting burnt during sunny and hot weather. The viewing is superior upstairs but you are exposed to the elements.
Here is a photo I managed to get of a San Francisco tour bus and the state seal on the symphony hall. I hope my kids correct me if I got that building wrong.