Old Caz is a beautiful and challenging 302Km (188mi) counter-clockwise loop with approximately 5000m (16,500ft) of climbing, a dozen miles of dirt roads, and a river crossing. Starting in San Francisco, it traces minor roads in Marin County and the coastal mountains of Sonoma County, then returns to the city via a scenic and hilly 50-mile stretch on CA-1, the Coast Highway. It showcases some of the prettiest countryside north of San Francisco: rolling pastures and farms, redwood forests, fragrant stands of bay and eucalyptus, and spectacular coastal cliffs.

The ride begins by crossing the Golden Gate Bridge to San Francisco's northern suburbs. Don't miss the views from the bridge, and watch for herons and other birds in the marshes by Mill Valley. The first climb of the day, Camino Alto, is short and pleasant in the morning air. A few miles further north, White's Hill marks the end of suburbia: for 160 miles you will pass no population center larger than a few hundred people.

The course drops into the Lagunitas watershed, then climbs for a mile to Dixon Ridge before descending through redwoods to Nicasio. You now ride for many miles across rolling Marin countryside, much of it dairy pasture. You can pick out distant roads by the tall stands of eucalyptus used as wind-breaks.

Short rollers alternate with longer climbs. On a clear day, Wilson Hill rewards you with a view across Sonoma and Napa valleys to the hulking profile of Mount St Helena, 40 miles away. Similar views unfold near the top of Burnside Road. After a steep and bumpy descent to the hamlet of Freestone, the course enters deep redwood forest and climbs gently to Occidental, then descends to Monte Rio and the Russian River.

Old Cazadero Road begins a few miles beyond Monte Rio. A 3.7-mile climb, it gains 800ft in its first 1.4 miles alone (an 11% average, with much steeper sections). Enjoy the fragrant bay and madrone forest, and take in the views of the surrounding hills.

At the summit you must hop two gates and negotiate a 1.6-mile dirt descent to Austin Creek. In winter the trail is soft mud and it is not difficult to bomb down it at full speed even on a road bike, but by summer the surface is hard and rutted. Watch for fallen trees and loose rocks. Don't be afraid to walk. At the bottom, Austin Creek provides cool solace. Carry your bike across a field of small boulders and through a gate, then climb on packed gravel for a mile before dropping steeply to Cazadero.

Fort Ross Road is the course's second big challenge. It climbs Black Mountain, drops down to the Gualala River, then climbs again to the coastal ridge. The reward is Meyers Grade, a breathtakingly fast descent (more than one mile at 18% grade) with expansive views of the coastline.

Now you are on Highway 1, but not for long. Just south of the Russian River you take a left turn onto Willow Creek Road, one of the true highlights of this ride. The pavement gradually disintegrates, then disappears entirely as you tackle a 4.6-mile traffic-free dirt climb. Be sure to carry some momentum into the switchbacks, or you may need to walk.

After rejoining Highway 1 by way of Joy Road and Bodega, we take back roads from Valley Ford to Tomales. Valley Ford Franklin School Road, remote and beautiful, features three increasingly steep climbs. Don't miss the views of Dillon Beach and the northern tip of Point Reyes.

The course returns to Highway 1 and follows it for over 45 miles, from Tomales all the way back to the bike path in Sausalito. The stretch to Point Reyes Station is familiar San Francisco brevet territory: the road rises and falls along the scenic shore of Tomales Bay, alternating sheltered coves and windy bluffs. Look for dairy cows on the left and oyster beds on the right. But rather than turning inland from Point Reyes Station to Nicasio, as the traditional San Francisco 300K does, our route continues south across Olema Valley to Bolinas Lagoon.

The last real challenge of the day comes 20 miles from the finish. The road pitches upward from Stinson Beach to Steep Ravine and winds above coastal cliffs for 5 miles before plunging to Muir Beach. Sunset from this road is memorable.

The climb out of Muir Beach gains only 600ft of altitude, but with 177 miles in your legs it will feel like more. But now you're almost home: just a cruise through Sausalito and a short climb to the Golden Gate Bridge before your triumphant return to San Francisco.