For the passing visitor, however, a glimpse of this extraordinary painting is the highlight of a great rural walk just 15 miles south of central London. Drawing a seven-mile loop around the countryside south of Croydon, and within the metropolitan orbit of the M25, the Downlands Circular Walk offers a slice of rural tranquillity where you'll find secluded meadows, wooded hollows and the earliest known wall painting in England.
The trail is waymarked with the symbol of a greater yellow rattle, a rare wildflower that flourishes in the chalk-rich soil. The walk starts up on Farthing Downs before dipping down into Devilsden Wood. Here the lofty branches of mature beech, ash and yew rise up on either side and meet like the vaulted ceiling of some grand hall.
As you emerge from the woods into an open meadow, you are pointed along the "permissive path to Chaldon Church" allowing you to cross a working farm in "single file please". At the end of a field, hop over a stile into a dense copse of trees where you'll find the tiny, perfectly formed church of St Peter and St Paul.
Although there has been a church on this site since Saxon times, much of the existing structure dates from the 12th to the 14th centuries. It was early in this period that a travelling monk is said to have painted the mural.
The Ladder of the Salvation of the Human Soul and the Road to Heaven measures 17ft by 11ft and is divided in two distinct parts. The lower shows the torments and punishments of those who have committed the seven deadly sins - a powerful and disturbing image depicting, among other hellish scenes, naked figures being tossed into a cauldron by the three-toed, horned demons of the underworld. An altogether more ethereal crowd are at work in the upper half, which is devoted to the salvation of souls. Running vertically through the middle to form a cross is the ladder to salvation itself up which the figures must climb, struggling with the demons who are trying to drag them down into damnation.
With only their mud-clogged boots to drag them down, weekend walkers have a much easier time, choosing either to cut back the way they came along the shorter three-mile route or to continue along the full seven- mile trail that winds across more farmland and on towards Alderstead Heath.
Following the latter, the landscape initially lacks the charm of the grassy meadows a mile or so back. But persevere and the route begins to regain its appeal as it joins the North Downs Way and heads along the ridge of the Surrey hills - with London's skyline on your left and a splendid view south over the Weald across to Boxhill.
Up until now it is almost impossible to lose your way if you follow the signs. The highest chance of getting lost is while trying to find the turning at Three Ways where the trail leaves the North Downs Way and heads back towards Farthing Downs. When you do find the right path, you might wish you got lost after all as you'll find yourself threading your way through a dreary residential area along what is probably the least engaging section of the walk.
It is not until you stumble over a stile out of Broad Wood and then rejoin the shorter route in the meadows of Hayfields that you start to feel your senses are being reawoken by the tranquil undulations of the Happy Valley.
Hindsight says perhaps you should have taken to the shorter route, but there is one consolation for tramping the full seven miles of this walk. When you are beginning to feel the winter chill in your bones, and your legs are tired from dragging muddy boots across miles of countryside, you'll find the road to heaven - a short detour along Trim Trail leading to the Fox Inn. And it's all the more enjoyable for the effort you have made in getting there.
Croydon tourist information (0181-253 1009) provides a leaflet guide to the walk with an adequate map. If you want something more detailed, then Ordnance Survey maps: 1:25,000 Pathfinder 1207 (Caterham and Epsom Downs) or 1:50,000 Landranger 187 (Dorking and Reigate) will help.
By rail, travel to Coulsdon South. A day return from Victoria or London Bridge costs pounds 4.
By car: from the A23 head east up Marlpit Lane and then take the second right turning along Downs Road. Continue for about a mile to the car park at the start of the walkReuse content