The Trolley tour of Savannah - and there are several to choose from - is an hour and a half of never-ending information.
We took the Old Town Trolley tour from the tourist welcome center on MLK. For a nominal fee, we were entertained and informed about the Historical Center of Savannah. There were 15 stops where we could jump off the trolley and wander around. About 15 minutes later (or multiples thereof) we boarded another trolley and resumed the tour. The 90 minutes of riding can be stretched into a whole day - so long as you are back on the trolley by 4:30PM for the return trip to the welcome center.
My favorite stop was at the City Market. We walked to the "Lady and Sons" restaurant, but chose not to wait for seating since there was quite a line. There are several restaurants and "bar and grille" establishments in the area, so food was easy to find. You can take your time eating and shopping before you go back to the trolley stop. River Street is a similar experience and a worthwhile one at that.
If you only have one day to tour Savannah, be sure to take the trolley tour.