Today, we went to the waterfall in San Ramon. It’s also called "Waterfall Cascada". (See "San Ramon Waterfall" entry.)
We decided to bike to the waterfall. It was only $8 for the bikes, and you get them for the duration of your stay. The bikes are all in great condition, thanks to the on-site bike shop at the hostel. All the bikes are nice 10-speed bikes, which is great for the unpaved roads and rocky hills. The bike ride from the hostel to the waterfall is only about 30 minutes. You will know the entrance when you get to it. It's hard to miss. There is a red gate locking the main driveway and matching gates across the street, locking up some fishing docks. A guard will come and open the gate, and you can just leave your bikes inside the gate without worrying about them.
If you decide to walk to the waterfall, it's about an hour to an hour-and-a-half walk, depending on your speed. There's not much else to say about that. I wouldn’t recommend this, just because that's a lot of walking and work in one day, all for only 30 minutes' worth of gratification. If you walk to the entrance, you will be worn out before you even make it to the waterfall. And then there is the walk back down and the walk back to the hostel. If you decide to walk, you turn a nice half-day trip into a full day of exhausting work.