There are all sorts of great trails just across from the GGBridge, either amongst the hills of Mt. Tam, or along the shoreline in Pt. Reyes. Those are two of my favorite hikes :)

Could I suggest the beach side of Big Basin park going up to the water fall in the redwoods
the entrance is just south of Anno Nuevo State Beach at Waddel Creek.

You should probably define "really long."
I really love hiking all over Redwood Regional Park, traipsing in and out of the valley with the stream trail at the bottom...there are gorgeous ferny thickets and cool woods, especially at the North end, and between the stream trail at the bottom, The French Trail along the West hillside, the East and West Ridge trails along the top of either ridge, and the myriad quiet little trails (some quite steep) between the preceding, I can always improvise a lovely hike anywhere from three to fourteen miles depending on the time I have available. It is so wonderful to be able to get really into quiet woods SO close to the megalopolis! It's just a few minutes from 580 up Redwood Road (I believe its the 35th Avenue exit, just head east and turn left on skyline (you can enter from Redwood Road but if you park on skyline (see map) either at the West or North Tip of the park, it's free!
www.ebparks.org/files/EBRP...ap_full.pdf
Wow. Too much coffee today, I gotta get to work.
Cheers!