Travel Acheron, one of the five rivers that flows through the underworld, according to Greek mythology. Eco tour companies rent canoes and kayaks for trips down the river through gorges and valleys. However, the water is shallow enough, and the current weak enough, that you can wade and swim down the river in some spots. Locals recommend taking a boat to travel all the way out to where the river joins the sea. If you prefer to stay dry, then consider a tour on horseback near the riverbank or a zipline tour through the trees.