It helps to have a good title, like "Good route near Charleston SC", and to spell the names correctly: Summerville and Folly Beach, correct?

I don't know the area. I like to use Strava to help plan a route using popular biking roads.

Here's a route made with the free Strava Route Builder. It's interesting how few options there are to cross the rivers down there. Summerville to Folly Beach.
You could draw a route that goes through Charleston instead of this rural route.

See the local view of the Strava Heat Map that shows popular biking roads, from a year's uploaded GPS recordings. (Click "Toggle Labels" to show towns and road names.)