From Belingham drive south into Larrabee state park and park at the parking lot near the boat Launch.  This will be the first parking lit south of the boat launch.  You need to pay the fee to park here.  Park and walk to the band shell where concerts are held.  Walk under the railroad tracks to access the beach via a tunnel.  You will come to the first bouldering areas at the beach here but the best spots are about 10 minutes walk south along the shore.