Since early times there had been an open-cast quarry on the side of the hill for mining chalk for the foundations of houses in the village and for roads; it is shown in one of Hannan's paintings of the 1740s. Sir Francis, the 2nd Baronet, set about extending this quarry in order to relieve serious local unemployment caused by three successive harvest failures in 1748, 1749 and 1750, and to provide material for a new main road between West Wycombe and High Wycombe. The men were paid one shilling a day, enough in those times to keep body and soul together. The old road ran along the valley bottom and had become so deeply rutted that carriages frequently overturned, especially during wet weather. The new road, which was on a straight line to Wycombe, was also intended to provide a three-mile vista of the church tower capped with its glittering golden ball on top of the hill.
The Dashwood Mausoleum was added a few years later, and the intended view he created is still very much evident today. The project was very much in keeping with the proposals which Sir Francis had already introduced into Parliament during his time as Chancellor of the Exchequer for stimulating the creation of work to relieve rural unemployment. He could easily, however, have just enlarged the existing quarry for this work to achieve the same ends, which would have been the obvious thing to do. We are not entirely sure of the reasoning behind his decision to dig a long winding tunnel a quarter of a mile into the hill with all sorts of chambers and divided passages leading off it and a huge room half way down. One can only presume it was an element of mischief and a fun project to undertake. The design is clearly symbolic and is thought to have something to do with the Eleusinian mysteries of ancient Greece. He was no doubt inspired by his travels on his Grand Tour when he would have visited other similar caverns and tunnels.
Many of the new landowners at the time were creating large estates and building impressive houses, and adorning them with all the latest fashion and artwork. There was intense rivalry between them, and Dashwood was probably keen to outdo his neighbour, Lord Temple, at Stowe. Whereas many of them were creating all sorts of amazing wonders above ground, he would be the first to do so on such a scale underground. Another much smaller cave was also dug out close to the small studio house outside Marlow on the road to Medmenham which was occupied by Giuseppe Borgnis, the painter whom Sir Francis had brought over from Italy to decorate West Wycombe. But it is unlikely that either of these caves had any pseudo-religious significance. It is true that there were anti-religious cults in northern Italy at that time as well as Masonic societies in Rome and Florence, but there is no evidence that Borgnis, who was a prolific painter of church interiors in his local area of Craveggia near Milan, was involved in any of these. Follies and artificial caves were fashionable - Horace Walpole had built a cave at his London house, Strawberry Hill, and had purloined some stalactites from the natural caves at Wookey Hole in Somerset, and there were many other examples such as those at Stourhead and Stowe - but Sir Francis's artificial cave is the largest and most curious of all. Over the arched entrance to the cave, he created a tall flint facade with a vaulted window which was divided by two slender stone columns. On either side of this facade are high walls of flint, with arches and recesses for statues, which encompass a large open courtyard. From the house across the valley, this was clearly intended as another feature in the landscape - this time a Gothic church.
When the late Sir Francis Dashwood was a child, the family used to make occasional expeditions to the Caves. The key to the heavy oak door, which was at the end of the brick tunnel at the entrance, was kept by Mr Fryer who lived in the house opposite. Mr Fryer charged a few pennies and in return handed over the key and some candle stubs. Sir Francis's father, Sir John Dashwood, had stipulated that part of the proceeds was to go towards the upkeep of the church. Although the Caves seem to have been open to visitors ever since they were built, it was really only locals who knew about them and they attracted few and were in a terrible state. The entrance was protected by the remains of the original iron railings, with barbed wire filling the gaps. The flint-faced arch and columns over the entrance tunnel had been knocked down at the beginning of the war on the orders of the Estate's land agent, Captain Hill, to form a barricade to protect the villagers from a bomb blast, as the Caves were intended to be used as an air-raid shelter. No maintenance work had been carried out in the Caves themselves since the eighteenth century; the main passage was littered with small lumps of chalk and in one place was half-blocked by huge boulders which had fallen out of the wall. In the Great Hall chalk lumps were scattered all over the floor amongst puddles of water, and the River Styx was full of enormous boulders which had fallen from the ceiling. Sir Francis formally re-opened the Caves in 1951 at a charge of one shilling and with candles provided free. A wave of publicity ensued and visitors started to roll in, especially when the local vicar, Father Allen, told the Daily Mirror that 'my tummy wobbles like a jelly every time I pass the entrance.' He followed this with a sermon denouncing the evil influence which emanated from the Caves. Sir Francis took exactly the opposite view. If there was any evil in the Caves, he felt it would soon evaporate when the place was subjected to the eyes of crowds of sceptical visitors; the worst solution was to bottle it all up by keeping the Caves shut and lending credibility to such stories. There have however always been tales of ghosts inhabiting the Caves ever since they were dug..
At weekends, debutantes who had come to stay often helped by selling soft drinks at the entrance, and by the end of that first summer nearly 10,000 visitors had paid their shilling and the Caves had made a tiny profit. It was better than nothing and seemed to offer scope for the future. The following year much work was done to improve the Caves and various surveys carried out, particularly in the Banqueting Hall which was considered unsafe at the time due to the danger of falling of chalk. Each came up with conflicting advice until an engineer from Yorkshire advised digging a new tunnel by hand, bypassing the Great Hall. An advertisement in the local newspaper produced an ex-Sapper, Jim Powney, who had been with the Guards Armoured Division. Jim agreed to come and work at nights and at weekends with another friend, Les Lawrence, and to dig out a tunnel 150 feet long by hand for £350, in order to bypass the Great Hall which was clearly the main danger. Jim and Les took about four months to dig out the tunnel, depositing all the chalk in the Great Hall and raising the floor level by four or five feet. Sir Francis used to help too at weekends, although using a pick was hard work. After the tunnel was finished, Jim and Les erected pit props all the way down the Caves wherever they were needed. Electric lighting was installed, the wooden pit props were replaced over the years with steel ones or brick tunnelling an elegant cafe was erected at the entrance, designed by Guy Shepherd who had previously designed Schweppes Grotto for the Festival of Britain Fun Fair at Battersea. Waxwork scenes were erected and a commentary installed with sound effects. Although rudimentary by today's standards it was, in fact, the very first underground 'sound and vision' programme in the world. Work was then undertaken to make the Banquetting Hall completely safe. The solution was to drill holes 130 feet down from the top of the hill into the Great Hall. Wire ropes were to be lowered down these boreholes and attached to a protective steel canopy which was to be hoisted up to the ceiling. Then 300 stainless steel bolts 10 to 15 feet long and with large plates at the end were drilled into the chalk ceiling and walls to make the chamber absolutely safe. One of the first visitors to file through the Great Hall after it was reopened in 1974 was a Mr William Brooks of High Wycombe. He discovered a lump of chalk in a crack in the wall and embedded in it were various coins dating from 1720 to 1754 as follows:- A George I silver shilling 1720 Two George II farthings 1730 A George II halfpenny 1733 A George II halfpenny 1751 Two George II farthings 1754 Since 1951 the Caves have attracted around two and a half million visitors, and many of the profits have been handed to various charities, including the National Trust to help pay for restoration and maintenance work in West Wycombe.