Coban Rondo Waterfall drops about 30 metres on the slopes of Mount Panderman, west of Malang. The falls are the main draw, but the approach is part of the trip: the road from Sepalu passes through green, hilly country with good views.
For a more satisfying visit, get dropped at the Sepalu turnoff and walk the last few kilometres to the waterfall. It turns a quick photo stop into a small excursion, and gives you a better feel for the landscape around Batu and Malang.