Lonely Planet warns that the mere mention of Badaling sends a shudder down the spine of hardcore Great Wall walkers. But as a starting off point to understand the wall's significance, it is easy (and cheap) to get to ... once you have grappled with the intricacies of the journey...
"An Englishman in Beijing" by Brian Salter (ISBN: 9781784779658) is available for sale in China at ¥85 from Taobao: https://detail.tmall.com/item.htm?id=675304960828&spm=a21dvs.23580594.0.0.3f062c1bQ6bPG5&skuId
** A Blogger's Guide to Beijing by Brian Salter, is published by Amazon ASIN: B083V1JQN5