The Sussex Ouse Valley Way is a 42 mile long distance walk that runs from Lower Beeding, a small roundabout south of Horsham (with pub attached) to the outskirts of Seaford (very near the station of Bishopstone (so empty that rabbits graze on the platforms). If one attempts to do this in a day, then the distance meets the criteria for a challenge walk (an echo of a conversation with Lev Babiev haunts here).
When one commences these walks, there are two directions to choose: from sea to source or vice versa. The official version is quite clear: start at Lower Beeding and proceed downhill. Undertaking this in late September when the light fails before the dark has some advantages. The route into Newhaven and Seaford runs along clear paths and mostly through lit towns: not a bloody forest (where the chances of getting lost rise significantly!). Yet, taken in a more philosophic sense: the source is the primary goal of any quest. You are walking up the river to discover something. This discovery contrasts with the less exciting goal of arriving at the sea. Arrival is a goal but doesn't quite embody the same promise. (The whole debate for this path is somewhat academic as the Ouse appears to vanish some fifteen miles before the end, though the source is listed as Lower Beeding.
The walk is a pleasant meander through Sussex: mainly flat with ponderings on various hills, downs and woods, rending a pleasing variety of terrain and stiles. Though the stiles became more painful later on in the day. The website of the organisers tells it far better than myself.
A challenging and grulling one day, especially with the night hike section.