* London's sewers and water mains are recreated in the Kew Bridge Steam Museum in Brentford Tel: 020 8568 4757 www.kbsm.org
* Williamson Tunnels in Liverpool stretch for miles around the house of the tobacco merchant who built them in the 19th century Tel: 0151 709 6868 www.williamsontunnels.co.uk
* Close to Royston town hall, Hertfordshire, is a cave that is thought to have been a hidden chapel for the Knights Templar Tel: 01763 245484 www.showcaves.comenglishgbmiscRoyston.html
* The West Wycombe Caves in Buckinghamshire were notorious as the meeting place of the Hellfire Club in the 18th century Tel: 01494 533739 www.hellfirecaves.co.uk
* Scotland's Secret Bunker in Troywood near St Andrews was part of a chain of Cold War underground early-warning radar stations.
Tel: 01333 310301 www.secretbunker.co.uk
* Dolaucothi Gold Mines near Lampeter in Wales date back almost 2,000 years and can be visited on guided tours Tel: 01558 650177 www.nationaltrust.org.uktraveltradepropertydetails.cfm?property_id=215
* Edinburgh's underground city can be found beneath the South Bridge Tel: 0131 557 4700 www.auldreekietours.co.uk