Take U.S. Hwy 70s north out of McMinnville, TN and go about 15 miles. Look for brown state park sign and turn left on Rock Island Road and follow the signs. To park near Great Falls, go past the lake and take the first left turn and follow that road to the end.
The boulders at the bottom of great falls are large and often wet from the spray from the falls. Be careful of your footing...it's easy to slip. Great Falls is roughly 100 feet tall and flows year round as it is fed by the resevoir above the dam at Rock Island.