Got ideal place for underwater drone, was talking about it Sunday night after a site visit, although that drone there is a bit big, so maybe not ideal then! Cwm Cipwrth copper mine. Three flooded shafts, one a winding shaft down to 15 fathoms maybe, one possibly blind, the other possibly also down to winding level. No drainage adits (there is an adit, but it's separate working above shaft level), so nothing's been seen in there for probably 150 years. Was thinking more in terms of the Martin Zero approach of lowering a camera into shafts (railway tunnels in his case) from a fishing rod!