Located just a few kilometres south of Batumi, Gonio is home to the Gonio-Apsaros fortress, a Roman-Byzantine fort that impresses by its sheer size. There is not much to see inside — fruit trees, mostly — so it is not strictly necessary to go in. The pebble beach south of the fortress is the cleanest swimming on the Adjaran coast.
If you do, don't go too early since the guy with the tickets doesn't get out of bed very early. He lives in one of the buildings opposite the fort, and there is always someone willing to wake him up for you. The guide doesn't do much talking and only speaks some Russian and Georgian.
The road continues south to the border at Sarpi, from where you can cross into Turkey. Frequent minibuses (no. 142) run from Batumi.