Hi Wim,
I don't really know anything about organised holidays. If walking in Snowdonia, I think most people would have a base hotel in maybe Llanberis or Betws-Y-Coed and go on day walks. Here are a couple of sites I found (although I can't vouch for them) wild-about-wales dot com/walking_holidays
snowdoniamountaineering dot com
wim commented on 12.08.12
25 porches on the counter
wim commented on 12.08.12
as in nature which brings me to a question: we would like to walk several days in nature in wales, organised perhaps, with a guide, with luggage brought from one place to the next. Horse, any idea where to search? you can mail me if you want to, wim at deskundige dot be