The website http://cymru1914.org/ gives a brief description of the contents on offer on it’s front page, I can’t do any better than replicate it below !
This project has conducted mass digitization of primary sources relating to the First World War from the Libraries, Special Collections and Archives of Wales. The project will make available a coherent, consolidated digital collection revealing the often hidden history of the First World War as it impacted all aspects of Welsh life, language and culture. This digital archive brings together source materials that were previously fragmented and frequently inaccessible. This digital archive is a unique resource of vital interest to researchers, students, and the public in Wales and beyond.
Wow if you have Welsh ancestry then you will have plenty to search, view and enjoy over the holiday period.