work following the best "seam" of stone, avoiding imperfections and master joints. The tunnels had, therefore, originally been unregulated "slot quarries" for sandstone, used for prestige buildings in the rapidly-expanding Liverpool of the Georgian era, and by subsequently vaulting them over Williamson was able to restore ground levels, facilitating his extensive housing developments on the site. While during Williamson's lifetime it was locally rumoured that he was earning large sums from unlicensed quarrying, Williamson had apparently claimed that he made little money, using extracted sandstone largely within his own properties. It seems possible that his secrecy was at least partly driven by a need to conceal his avoidance of both large amounts of income tax and mineral rights duties due to the West Derby Waste Commission from the sale of sandstone. Knowledge of the latter dealings may have been the reason behind Henderson's threat to sue James Stonehouse. Despite retiring from the tobacco trade in 1818, Williamson left an estate valued at £40,000 - the equivalent of around £3.3 million in 2019 - and it appears that a large proportion of this income must have come from his excavations and subsequent property development. The Joseph Williamson Society and Heritage Centre The Joseph Williamson Society was founded in 1989. It was incorporated as a private limited company in 1996 and acquired charitable status in 1997. Its aim is to promote interest in the life and philanthropic achievements of Joseph Williamson and takes the form of talks, tours, publications and educational visits. In autumn 2002, after much excavation, removal of rubble and renovation, one of the three sections of the site, the Stable Yard section, was opened to the public as the Williamson Tunnels Heritage Centre () under the trusteeship of the Joseph Williamson Society. Visitors are taken on a guided tour which includes the south tunnel and the double tunnel and various artefacts are on view including some of the items which have been uncovered in the excavations. A programme of events and entertainments is organised on the site. The entry to the heritage centre was formerly part of the Lord Mayor's Stable Yard which closed in 1993. The stable became the home for a horse again when Pop arrived in 2003. Public Access The Heritage Centre allows visitors to see a substantial section of the tunnels, including the impressive "Double Tunnel". They are open Tuesday-Sunday during the summer months (Thursday-Sunday