From I-405 Northbound:

Exit freeway at Exit #17 (NE 70th St.)
Turn right at end of freeway exit onto 116th Ave. NE
At NE 60th St. Stop sign, continue straight ahead
Park entrance is on the left hand side of the road.

From I-405 Southbound:

Exit freeway at Exit #17 (NE70th St.)
Turn right at end of freeway exit onto NE 70th St.
At light, turn right onto 116th Ave. NE
At NE 60th St. Stop sign, continue straight ahead
Park entrance is on the left hand side of the road.

Closer view