We went to San Cipriano this weekend. It's a crystal clear river in the jungle almost at the end of the highway that pases Kilometro 18. It's two and a half hours by bus and about ten miles before you get to the outskirts of Buenaventura. From the parking area you have to ride on a really little wooden cart called a "brujita" set on the railroad tracks for six kilometers with a "gondolear" poling you along, four people sqeezed on and keep your feet up since it wizzes along at about 30mph on the downhill slopes. At the end of the line is a little jungle pueblo ranged along a moss covered oil pipeline where you can rent truck type inner tubes for five thousand pesos. You hike another kilometer or two down the pipeline to where it's convenient to put the tubes in. A short cut involves walking on top of the oil pipe for about fifty feet crossing a ravine. Better have good balance, the ravine is kind of deep and the pipe is slippery with moss. The river is great. A sign says at some points it's over ten meters deep, hard to believe but so clear I could almost always still see the bottom. There are some fast moving stretches of rapids that are fun but you better keep your arse up to avoid getting womped by the rocks (which happened to my wife who is now dead set against such outings...at least for the moment, but she recovers quickly and needs to get toughened up anyway for our upcoming trip around Peru).
You can overnight at a couple of "hotels" in the village too but they're barebones basic, little cubicles made of wooden slats with a bed and one bathroom for everybody. Not reccomended for the sqeemish. As always bring your own "papel higenico".
San Cipriano is quite a tourist destination on weekends and pretty safe since the area is controlled by the paramilitarys (many of the men you see in the village are weekday warriors I was told). Among other things they protect the pipeline. Mid week though is a different story and not a good time for a foreigner to be in the jungle there. The same goes for the highway as mid week is when the guerrilla sometimes make trouble on it setting up temporary roadblocks to see what they can catch then clearing out just before the army comes along.
