Lovely Kawah Rengganis (also known as Kawah Cibuni) is a pretty, isolated river fed by hot springs and surrounded by billowing steam from volcanic vents. It's off the main tourist path and is wonderful for bathing. You have to park by the road and walk for a few minutes up to the pools; villagers here ask visitors for a 50,000Rp donation to visit their land. It's best to avoid wearing skimpy swimwear when bathing here.
It's around 20km southwest of Ciwidey and is hard to reach without private transport.