This ancient cave system has been mined for over 4000 years. You could take the self-guided tour or delve deeper. There are semi-deep and deep visits available which can be booked with experienced guides.
Today, the iron ore is used in ochre for paints etc. Regular events are held inside the caverns too, such as theatre shows.
There are nine caverns to visit in the self-guided tour and an interesting display about the history of the caves and mining at the entrance in the museum.
Wikipedia describes the caves and more detail can be found on the official website: visit link
'Clearwell Caves, at Clearwell in the Forest of Dean, Gloucestershire, England, is a natural cave system which has been extensively mined for iron ore. It now operates primarily as a mining museum. The caves are part of a Natural England designated Site of Special Scientific Interest and the notification includes parts of Clearwell along with Old Bow, Lambsquay and Old Ham mine complexes.
Mining
The caves were formed by underground streams around 330 million years ago. They have been mined for iron ore possibly as far back as Roman times and extensively in the last century, which considerably enlarged and extended the network of natural caverns. Ochre has been mined here for even longer.
The nearby scowles at Puzzlewood represent similar shallow mines which have been exposed from above.
The mine is still worked intermittently to produce coloured ochres for use as natural pigments. These are milled and sold in the mine's own shop. A range of colours is available, from pale yellows to near-black, including of course the commonplace red ochre. Clearwell is also known as one of the few locations where the rare purple ochre may be found.
Nine chambers are easily accessible from ground level, and represent the earliest and most complete workings of the mine. A network of much deeper chambers does exist, but can only be visited in the presence of a guide and with appropriate caving clothing for safety. The upper caves are open to the public without special equipment.
Recreational use
The caves have been used as a Santa's Grotto at Christmas time for many years, for easter egg hunts and in the summer barbecues, concerts and theatrical performances have been hosted in the upper caves. One chamber is large and well-ventilated enough to permit underground cookery.
Parts of the Doctor Who episodes "The Christmas Invasion" (2005), "The Satan Pit" (2006) and "Time of Angels" / "Flesh and Stone" (2010) were filmed in the caves. The nearby quarry at Clearwell has also long been used for filming science fiction scenes, such as in Blake's 7.
Reported paranormal activity
Claims of paranormal phenomena at the caves have been made over the years. These include reports of the sound of metal clanging in the distance and the existence of 'paranormal' orbs, which appear on flash photographs, which are nothing more than the refraction of light on airborne dust and water particles.'