There is lots to see above ground and some underground parts can be seen without any climbing gear or skills, however just the walk up alone is staggeringly beautiful and makes a visit worthwhile for the scenery alone, one of the adits is a bit of a squeeze and not for the chubbier explorer , here is a PDF that points out what levels are accessible with and without SRT kit https://www.aditnow.co.uk/documents/Ratgoed-Slate-Mine/Ratgoed-Slate-Mine.pdfDo you need climbing gear to get in or can anyone scramble/walk down?
obviously if you are going underground you need a twat hat, headlamp, torch, call out etc, you know the score ... but if you are going just for the sheep then send Lenston a PM he knows them all by name now