If you are considering walking this route yourself, please see my disclaimer. You may also like to see these notes about the maps and GPX files.
I turned left along the path, following it a short distance through a narrow bit of woodland. Beyond the wood, the path continued between widely spaced fences with paddocks either side, and then between a fence on the left and a hedge to reach Bottom House Farm Lane (there was new road here, presumably an access road for people working on HS2). Beyond the lane the path continued along the valley bottom. After a few hundred yards the path followed a tall hedge on the right for a few hundred yards. All the time there were arable fields sloping uphill on my left.
The path along the Misbourne Valley
The path along the Misbourne Valley
The path along the Misbourne Valley, approaching Bottom House Farm Lane
The path along the Misbourne Valley, after crossing Bottom House Farm Lane
The path along the Misbourne Valley
The path along the Misbourne Valley
After the hedge on the right ended, the path continued along a track with neither hedges nor fences. Just after a hedge started on the left, I came to a path junction where I took the path going half-right across a corn field. On the other side of this field I went over a footbridge across the river Misbourne, then turned left along the edge of another arable field, close to the river on my left. Beyond this field, the path stayed close to the river and soon went under a graffiti-daubed road bridge. Finally the path followed the edge of a meadow to reach a road on the edge of Amersham Old Town. I turned left along the road, then turned right at a roundabout. After maybe a hundred yards I took a footpath on the left, that was soon running close to the tiny river again. I went over a footbridge to reach the back of a Tesco supermarket, where I turned right (with the river now on my right) to return to the car park where I'd started.
The path along the Misbourne Valley
The river Misbourne from the footbridge
The path to Amersham alongside the river Misbourne
The path to Amersham alongside the river Misbourne
The river Misbourne
The path to Amersham alongside the river Misbourne
The river Misbourne
The path to Amersham alongside the river Misbourne, after going under the road bridge
The path close to the river in Amersham Old Town
This was a very pleasant walk, and I was glad that I'd patiently waited for the rain to stop at the car park in Amersham rather than turn round and drive home (which I'd seriously considered) - I didn't have any rain during the walk at all. The section through Penn Street, Winchmore Hill and Coleshill is one that I've walked so often (there are no viable alternatives) that I always worry I'll find it boring, but that wasn't the case at all today (thanks to the pandemic it's been a while since I last did it). The path through the Misbourne valley is also one I'm possibly a little too familiar with, but by starting at Amersham so that it was split between the beginning and end of the walk, this again wasn't an issue today.