Goa Tetes is a wet cave and waterfall route on the same rough side of the valley as Tumpak Sewu. Water trickles and pours over orange-brown limestone, forming shelves, small pools, and slick passages that feel more like a natural obstacle course than a formal sight.
It is best combined with Tumpak Sewu while you are already in the gorge area. Expect wet feet, slow footing, and plenty of spray. In the rainy season, check locally before going down; the fun disappears quickly if water levels are wrong.