I spent last night on Ancestry tracing a great uncle who died in WW1. He died and is buried in Rouen. I will be at our holiday home in Normandy next week and intend to visit his grave on Remembrance Day, it is a bank holiday in France.
Ancestry is great for all the military records, they are always adding more, recently one called 'soldier's effects' which I thought would list the belongings sent home after a death, but was actually a list of gratuities paid to dependent family members - I found a niece there that I didn't know existed and still haven't quite sorted out.
However Ancestry is only the start. By ggogling more widely I have also found out what actions his regiment and battalion were involved in, in the week before he died. I found details of the battle including a map showing exactly where his unit was.