The National Library of Ireland online catalogue is a brilliant creation!
The area I really like is the digitised glass plate images from their early photographic collections.
Once you’re on the site the first thing you’re likely to do is search against place names. We live in Ballydehob and my father comes from Glandore, my mother Graiguenamanagh, and it’s great to be able to see what these places looked like 100 years ago or so.
No need to write too much about it, better just go there and check it out for yourselves.