I visited The National Library of Wales as part of a mini trip whilst I was at library school last month. It is very grand and posh outside and also contains a large hill to walk up. I found that Aberystwyth was one massive hill but that is for another time.
A bit about the library from their website;
https://www.library.wales/about-nlw/about-us/about-nlw/- accessed 20th April 2019.
Go HERE to learn more about what you can see and do inside, HERE to see the Welsh film archive pages and HERE to search the collections the library has.