I toured the battlefields in 2014 and one incident stuck in my mind. Standing on the Allied ridge, roughly where Mercer's battery was, my older son and I watched a small group of horse riders crossing the valley from the French side. I told him to keep an eye on them as they crossed the bottom of the valley, having an idea that they would "disappear" from view due to the undulations. However, even I was astonished at how long they remained out of sight and how much closer they were when they reappeared.

If you are planning on "flying solo" rather than going as part of an organised tour, I can highly recommend David Buttery's "Waterloo: Battlefield Guide" which covers all the actions of the campaign, and provides access instructions to all the areas still accessible to the public.