Well I thought they were only on Sundays, so thanks for checking!
If they're like the family rides that they do once a month (which I highly recommend, btw), then you ride to a spot, stop and talk about something historical, ride to the next spot, stop and talk, ride, stop, ride, stop, etc. So definitely not a sustained cardio effort.
I don't know how you've done your rides in the past, i.e., if you like to ride around the sites with few or no stops or if you stop frequently to check things out.