Will be overnighting in Savannah to catch early flight the next morning after a few days on Hilton Head in August. Any suggestions as to how to spend an afternoon in Savannah?

Walk on the quaint main street down by the river and have some pecan pie! There is also a trolly-type tour that will show you around the city which is very attractively laid out on multiple squares.

Have dinner at the Pink House.

Steer clear of hard-hearted Hannah.

Start with one of the trolley tours, then walk as many of the residential squares as you can in the daylight. That is the essence of Savannah! River St, historically, was the CBD of Savannah but now is not much more than a conglomeration of tacky tourist trap shops, housed in the old cotton warehouses. Still the river traffic is interesting and there is lots of history, including the cobblestones paving the street which had been used as ballast in the ships coming over, so it's still of interest, but I'd spend more time in the squares. Some of the prettiest are Monterey, Madison, and Chippewa Squares, all in a line running down Bull St, culminating in Forsyth Park with it's beautiful 3 tiered fountain. You'll pass Jones Street on that route, and it's worth a detour of it's own. The entire length is beautiful.

Go to the visitors center, book a narrated tour for a fascinating tour of a gorgeous city. You will get the local history and quaintness with a guide

All of the above suggestions are excellent. And what OliveOyl has to say is quite true. We were in Savannah and thoroughly enjoyed the trolley tour, and then if time permits, enjoy walking around the squares. Do take a bit of time and see the Riverwalk, but we much preferred the squares and seeing the arcitecture.
In the evening we took a qhost tour...it was fun...
Enjoy.

Thanks, everyone. Now I have a question about where to stay but will post a separate question.