Northern Vancouver Island has a number of limestone formations and caves. Not too far from where I live is an interesting geological feature the locals call the "Eternal Fountain". Essentially an underground river flows to daylight and falls into a pool about 20 feet lower, from that pool the water flows back into another cave which leads back the direction the river came from in the first place only on a lower level, all very curious!
I actually used a tripod for todays pictures as it was fairly dark under the forest canopy. On the bottom picture I set the aperture to f22 to slow the shutter speed down to get that silky look to the flowing water.