Though locals primarily know Skidaway Island as the site of The Landings, the first gated community in Savannah [1], for your purposes Skidaway Island is notable for two beautiful and educational nature-oriented sites.
The first, the University of Georgia Marine Educational Center and Aquarium (30 Ocean Science Circle, 912/598-3474, www.uga.edu/aquarium [2], Mon.–Fri. 9 a.m.–4 p.m., Sat. 10 a.m.–5 p.m., $4 adults, $2 children) shares a gorgeous 700-acre campus on the scenic Skidaway River with the research-oriented Skidaway Institute of Oceanography, also UGA-affiliated. It hosts scientists and grad students from around the nation, often on trips on is research vessel, the RV Sea Dawg.
The main attraction of the Marine Center is the small but well-done aquarium featuring 14 tanks with 200 live animals. Don’t expect Sea World here; remember you’re essentially on a college campus and the emphasis here is on education, not flash.
The second site of interest to visitors is Skidaway Island State Park (52 Diamond Causeway, 912/598-2300, www.gastateparks.org/info/skidaway [3], daily 7 a.m.–10 p.m., $2 parking fee). Yeah, you can camp there, but the awesome nature trails leading out to the marsh—featuring an ancient Native American shell midden and an old whiskey still—are worth a trip just on their own, especially when combined with the Marine Education Center Aquarium.
To get to Skidaway Island, take Victory Drive (Hwy. 80) until you get to Waters Avenue and continue south as it turns into Whitefield Avenue and then the Diamond Causeway. The park is on your left after the drawbridge.
An alternate route from downtown Savannah [1] is to take the Truman Parkway all the way to its dead end at Whitefield Avenue; take a left and continue as it turns into Diamond Causeway into Skidaway.
Links:
[1] http://www.moon.com/destinations/charleston-savannah/savannah
[2] http://www.uga.edu/aquarium
[3] http://www.gastateparks.org/info/skidaway