I am a little disappointed with this book, as it is not what I had expected, but this is partly my own fault for not taking advantage of the 'inside look' feature on Amazon, but I purchased it after seeing it advertised with a little bit of blurb in The Guardian.
From the title 'Wild Gym: Join the DIY Exercise Revolution: 50 Ways to Get Fit Outdoors' I'd expected the book to be a guide to exercises you could do outside instead of going to the gym, and the 'DIY' bit suggested to me that it would be stuff you could do outside by yourself for free: ie the best outdoor, DIY equivalent of going to the gym to excerise.
However, the book is more of a collection of brief introductions to a variety of outdoor sports; this would probably be useful to look through if you need some inspiration about what new sport to try or are looking for a new hobby. But without the right money, transport, time, access to equipment and appropriate venues / locations and hire shops, the majority of these activities aren't practical options for many people... falconry, golf, dog sledding, skiing, fishing, recumbent cycling, horseriding, streetluging, landyachting, sailing, bowls, potholing and loads of other activities are featured with a brief overview, nice photos and sources of further information but I don't think the book's content are well represented by the title and the cover.
Though of course I should've done a bit more research before buying 'Wild Gym' and some people with no idea of what activities they'd like to try may find this kind of book useful, it wasn't at all what I was expecting and I think this expanded list of sports / activities is pretty pointless for the majority.