Pacific Grove is in a unique location at the tip of the Monterey Peninsula, so access is limited by geography. To make matters even more difficult, between PG and Monterey is the US Army's Presidio of Monterey with no public access, and between PG and Carmel you have Pebble Beach with limited public access for a fee. So there are really on two public (& legal) ways into PG from Highway One. From downtown Monterey Lighthouse Avenue is 2 lanes in each direction, under the Custom House Plaza tunnel, through New Monterey, and putting you at Central Ave in downtown PG, one block from PG's own Lighthouse Avenue.
From the other direction near Carmel, you can take State Highway 68 (Holmen Highway) from Hwy 1 into PG. This route is a narrow, twisty, 2-lane route that cuts between the Presidio of Monterey and Pebble Beach while passing through the Del Monte Forest. Upon entering PG you are on Forest Drive which leads you into downtown PG. A left after the shopping centers puts you on Sunset drive and takes you to Asilomar Beach and beautiful Ocean View Drive. During the local "rush hour" Hwy 68 can get very busy where it meets Hwy 1 and at the entrance to the Community Hospital of Monterey Peninsula (CHOMP!), so the city is planning to improve this route in the near future (http://www.monterey.org/publicworks/holman_hwy/description.html).
And since PG has no airport, no public docks or boat ramps, and no railroad, the only other way into town is walking or biking along the Monterey Bay Coastal Trail.