I think I know the answer - my plan is "not possible". But, before I totally dismiss the idea, I thought I'd throw this out there to see if someone in this community might know the answer.
Here's what I wanted to do:
I wanted to surprise my teenage daughters with an amusement park day, in the midst of our 10 days in Italy. The only possible time to do this is in the day of travel from Venice to Florence. We would have to leave our hotel in Venice really early in the morning (7:00) and catch a train to whichever station is nearest Gardaland (?). Four hours would be about the max we could handle at the park. Then I have to get to Florence to pick up a rental car (this is a Saturday, which means that I probably have to pick up the car at the airport rental company offices - which I don't know anything about train station/airport location). Then I need to drive to Siena before it gets too dark (arrive around 8pm-9pm?) so I can find the house.
I don't think there are enough hours in the day to make this possible. The only flexibility I have, is that I could rent the car in Venice (where?) and drive the distance, if this makes more sense. It will cost more, because I drop the car off in Florence at the end of the week.
If Gardaland is out of the question for this trip, do you happen to know if there any other amusement parks that might be on our path (around Frankfurt, Geneva, Zurich)? I'll have rental cars at all locations, and can drive up to 3-hours each way for day-trips.