For a fun 10k out and back, head a few miles north of Vancouver to the Salmon Creek Greenway. The paved multi-use path runs for 3.2 miles between Klineline Pond (a popular swimming spot) and NW 36th Ave., following the Salmon Creek. It’s a nice combination of open and wooded sections.
Note that for about 1 mile of the Greenway, toward the eastern end, there’s a parallel section that’s a more rugged gravel path. There’s also a short trail along the west side of Klineline Pond.