The B485 begins at a roundabout on the A413 Great Missenden bypass. The earlier route out of the town, via Church Street, was turned into a bridleway (part of NCN57) with a tunnel under the bypass; the current route is via a link road meeting the A413 at a roundabout just to the north. A new link road was built as part of the bypass, a sweeping bend that climbs fairly steeply up Frith Hill. After meeting the original route it continues climbing up the side of the hill, out of the Misbourne Valley. Fifty metres above the road's start, the land flattens out. While the land is flat, the twistiness continues, with bends warned of. Passing to the south of South Heath, the road straightens out. At the road's highest point, Hyde Heath Road heads southeast towards Amersham.
Church Street, Chesham
At Hundridge Manor, the B485 begins its descent. The road is cut into the side of the dry valley that is forming, with an artificial slope on the right, then goes down the valley at the bottom of it. Eighty metres below Hundridge Manor, at Halfway House Farm, the River Chess begins, and the valley floor becomes almost flat. While there was a sign welcoming you to Chesham halfway up the valley it is still some way before the urban area starts, and when it does it is set back from Missenden Road, on a separate, parallel road. After a couple of houses, still set a long way back but fronting directly onto the road, Pednorend ends and Old Chesham begins. The buildings are much older and closer to each other and the road, so close to the road that one of them takes out a lane. Just after that, at the Queens Head pub, it becomes Church Street. The road remains narrow for a while, just one wide lane, before becoming two again at The Bury. Passing the church (which newer dwellings block the view of), the road twists through the buildings before ending at the A416. Due to a barrier, B485 traffic cannot access, or be accessed from, the southbound lanes.
The Metropolitan line passing over the former B485 in Waterside
The eastern half of the B485
Until some time between 1978 and 1984, the B485 went further. There was a brief merger with the A416 and then it continued down the Chess Valley, through Waterside and then on to the A404 at Chenies. The half-mile nearest to Chesham has been made access only in the Chesham-bound direction, with a road on the south side of the river forming a one-way link for Chesham-bound traffic from beyond that part of Waterside (the road, not the part of Chesham). The whole of this section is now unclassified