This is a nice loop starting from Entrada Lodge that gets you to the river. Along the way, there are a few very nice views of the Cascades (Mt. Bachelor, Broken Top and the Three Sisters). It's a nice, flowing trail with a few technical bits, but relatively easy to ride or hop off your bike.
Start from the Entrada Lodge, or alternatively connect from the designated parking lot a little further on Century Drive. The trail flows nicely, with some up and down. There is one notable section of rocky uphill with two tight switchbacks (or downhill depending on your direction). You might want to scout it first if going downhill. That little uphill brings you nice views of the Cascades.
Then drop through a short rocky section and the river comes into view. This connects to the Deschutes River trail if you want to ride along the river. Otherwise, continue the loop back towards Entrada on a similar trail.
It's a nice introduction to Central Oregon riding.