If you do then you might be interested in the Londonists’s Subterranean map of London. Whilst this map includes features such as Cold War bunkers, abandoned Tube stations, buried rivers, deep level shelters, the more obvious features, they would be interested hearing from people with information about other features, although they do have a few rules about what is to be included and what isn’t. So to the view the map (see below) and to find out how to contribute to it please go to http://londonist.com/2008/03/subterranean_lo_1. *
You might also be interested in more details (primarily descriptions and pictures) on the Lost Rivers of London, at http://www.londonslostrivers.com/, a website based on Paul Tallings book. There is also the 2016 book however by Nigel Barton and Stephen Myers “The Lost Rivers of London (3rd Edition)” and in the past I certainly found the earlier 1992 Edition of this book useful.
*If link not working search www.londonist.com website using phrase “Subterranean London…mapped” and it is article from March 2008