I'm fairly certain we went when I was very young, would like to go again and take me metal detector this time.
I was there last summer, Jonno. The place has a malevolent feel to it, and I fear many sordid crimes took place in those caves. Many MPs, poets, artisans and other illustrious citizens would meet up down there to gamble, frolic with mistresses, and take part in other dubious activities. According to local myth, the Underworld can be accessed from the River Styx, and it was via this gateway that human sacrifices were made. All in all it is a fascinating place to visit, but if you want a day out in Bucks with the family, try West Wycombe Park at the bottom of the same hill. The Hellfire sandwich is lovely, though.