Hi,
It's been a couple of years since I was there (as part of a survey with Northern Mines Research Group) but it's a good trip with much potential. Water levels vary but it's rarely over knee deep (weather on top dependent of course). About a third of the way along the level, if memory serves, a collapse from an airshaft forces the explorer to lay out flat and wriggle beneath the boulders on the right hand side. It appeared then as stable as piles of boulders are, but you'd obviously want to get through without touching anything.
This small obstacle defeated, progression up the passage way is easy going, arriving at a picturesque stone arched junction. From here passages raidiate off an doubtless much fun can be had exploring.
You'll have noted the remains of the smelt mill a little way downstream of Hard Level - Old Gang. According to Arther Raistrick (The Mines & Smeltmills of Swaledale & Wensleydale - Vol 1, the mines), ready for smelting ore produced on the dressing floors adjacent to Sir Francis Level in Gunnerside Gill was taken up the valley and into through Bunton Level where it was trammed through the hill to exit via Hard Level and taken to the Old Gang Mill for smelting. Whether that route is still open, I know not, but it could be fun finding out.
There are few sources for the mining remains of Swaledale and apparently fewer surveys. Some information canbe found in Raistrick's books (mentioned above); Mike Gills, The Mines and Smeltmills of Swaledale and John Hardy's The Hidden Side of Swaledale. Rather unhelpfully all are now out of print and difficult to come by.