Long before Robin Hood and his Merrie Men reputedly holed out in Sherwood Forest to engage in guerilla combat with their arch-enemy, the Sheriff of Nottingham, a labyrinth of man-made bolt holes - more than 400 in the city centre alone - had been burrowed out of the soft sandstone on which Nottingham is built.
So much so, a biography of King Alfred written before 913 refers to the city by its Celtic name, Tigguo Cobauc (place of cavy dwellings), and in 1632 John Taylor described it thus: "a great number of the inhabitants (especially the poorer sort) do dwell in vaults, holes in caves... cut and dug out of... he Rock". In the early 1800s, self-styled Robin Hoods, the anti-Industrial Revolution Luddites, used them for hatching plots, and pubs have always appropriated them as storehouses, breweries and drinking cellars, some still in use today.
Discover more by going to the middle of Broadmarsh shopping centre, donning a hard hat and following the taped commentary - of two children escorted by the Spirit of the Caves - around a Second World War air-raid shelter, a cess pit, a well and Britain's only known underground tannery. You can see a Victorian slum dwelling, play Victorian pub games and view the remains of one of Nottingham's oldest streets, Drury Hill. A guided tour is available for groups if preferred.
Grimmest cave of them all is the County Gaol, established in 1449. It is situated in the impressive Shire Hall, now the Galleries of Justice, where 250 years of crime, punishment and law can be explored. New activities include getting "steamed up for laundry duty and dressed for a day's hard labour", attending a crime scene and assessing evidence using forensic science and computers.
On a high rock dominating the city is the Castle, established by William the Conqueror in 1068. Almost totally destroyed after the Civil War, it was replaced by a magnificent Ducal mansion in 1674 and has been a museum and art gallery since 1875. Here, too, secret passageways and caves lie hidden, including Mortimer's Hole, where Edward III's men seized Roger Mortimer, murderer of Edward's father and pretender to the throne. As former air-raid shelters, they provide the perfect setting for education sessions on the Second World War.
The six-strong access team plus 11 freelance educators provide an extensive programme for all ages. On my visit, freelancer Beverley McAuley is in the Long Gallery showing Year 4 pupils from Ibstock Junior School, Leicester, how to be archaeologists as part of a session on Ancient Greece. To groans, she says: "Imagine that you're in the Manchester United fan club and you have a little cup with the logo on and your favourite footballer, Dave Beckham. You love it and drink out of it every day. Then imagine Man U is relegated and Beckham goes to join Leicester City. You become Leicester City supporters and throw away your little cups - some get smashed, others after thousands of years lie deeply buried." These, she explains, will give clues to future archaeologists just as ancient Greek pots tell us about the clothes, hairstyles, gods and goddesses of the time.
The children interpret two paintings, "Heracles vanquishing Diomedes" by Charles Le Brun, dated around 1638 and "Homer singing The Iliad at the gates of Athens", by Guillaume Guillon Le Thi re, dated 1811. They also handle exhibits and search for patterns in the Greek gallery.
Also popular are Medieval Realms and Focus on First World War sessions for secondary groups and exhibitions such as "The Story of Nottingham", the Circle of Life ethnography collection, and decorative arts displays.
At the base of Castle Rock is Brewhouse Yard Museum, a row of 18th-century cottages, representing 300 years of social history. Beverley McAuley leads a "Through a Victorian keyhole" trail here for key stage 2 pupils.
Rock Cottage, next door, houses a 1930s schoolroom and toy shop.
Outside the city, the team runs workshops at Wollaton Hall, a fine Elizabethan house devoted to the hidden world of nature from insects to giraffes; Green's Mill, Sneinton, a fully operational windmill where groups can learn about its former inhabitant George Green, the 19th-century mathematician and miller, and try out the hands-on science centre's experiments with light, magnetism and electricity; and Newstead Abbey, Ravenshead, Lord Byron's former home.
No visit to Nottingham would be complete without looking in on The Tales of Robin Hood. I arrive to the clashing of swords just in time to witness Robin and Guy of Gisborne fighting to the death. Having vanquished Guy, Robin takes off his chain mail and answers questions. These dramatised storytelling sessions are a recent innovation to enhance the cable-car ride, an adventurous journey with Robin through medieval Nottingham.
There is also "The Case for Robin Hood", an audio-visual show about a "private dick" charged with "getting the dope" on the Robin Hood legend. Messages left by researchers on his answer machine build a picture of how the legend began and grew. An education pack supports KS1-3 history, cross-curricular work and tourism projects.
For more Robin Hood, go to the 450-acre Sherwood Forest Country Park, near Edwinstowe, and see the mighty "Major Oak", where, according to legend, Robin hid from the Sheriff, a video about the history of the forest and an exhibition on its wildlife.
Castle Museum sessions cost pound;40 per class; education packs are up to pound;5 each. For newsletter, tel: 0115 915 3692. Other details are in the Nottingham and Nottinghamshire Group Travel Guide available free, tel: 0115 915 5555 or 0115 977 4216