Another bad one:
Last year I followed someone's online route, little realising how much it could have changed in the ten years since it was published.
Towards the end, the footpaths and tracks were marked on the map alright, but I followed one for some way that was no more than a faintly-trod animals' path, then where it turned left at a gap in a wall and into a forest there was no sign of a path at all.
Starting off down an overgrown sunken way, I found it was blocked with trunks and tangled branches of a number of fallen trees. By the time I had worked an uncomfortable way around these I gave up and proceeded to the edge of the forest where I trespassed along the edges of fields. At times I saw footpath arrows marking the non-existent way inside the wood.
At the far end there was a short length of grass track and a bridleway sign on a post! But now I needed to head southwards on a forestry track, and when the course of this was eventually located - on the far side of a barbed wire-topped fence - it was impossibly overgrown with trees, shrubs and brambles coming up through the hard surface. I struggled for about fifty metres before extracting myself and working out a new route which, unfortunately, had to be mostly on minor roads.