While we were on holiday in Belgium we visited the In Flanders Fields museum in Ypres. It is one of the most thought-provoking, sad yet interesting places I have ever been. The whole concept and layout of the museum is guaranteed to have anyone (except the rude English teens who practically ran through it) in tears.
I would like to visit the Somme also, my Dad's uncle was blinded and deafened in the war and my Mum's uncle had his ankles machine gunned, both surviving but the things they had to deal with, the things they saw and experienced. Truly awful.
In Ypres there is a monument called the Menin Gate , wall upon wall of names of soldiers dead but never found. Over 54,000 names, too.