The Düden river runs down from the Taurus Mountains and across the plain on which Antalya is built. On its way it creates two very different waterfalls. Upper Düden (Yukarı Düden) lies inland, in the northern part of the city, surrounded by a green park. Lower Düden (Aşağı Düden) is where the same river reaches the coast and falls over the high limestone cliffs directly into the Mediterranean, in the Lara area east of the centre.
They are not next to each other, so treat them as two separate stops. Many visitors see only one; if you have half a day and your own driver, seeing both is perfectly realistic.