Pine Flats Hot Springs is a great mix of accessible and remote, undeveloped but comfortable. The short hike keeps the crowds down, but the trail is maintained and easy to moderate, depending on weather conditions.
If you’re looking for a place to stay and run, I recommend this stretch of the Centennial trail, between mile markers 9 and 11, from the Spokane Valley Hampton Inn and Suites to Mirabeau Park and back (or vice-versa). As you’ll see below, the trail is accessible and follows the Spokane River East and West. Surrounded by lush growth and just over a small rise that separates the trail from the commercial development of Spokane Valley, the Centennial Trail feels far more remote and isolated than it is.