The National Archives is in the old Jacob's Biscuit Factory, which was occupied by the rebel forces during the Easter Rising in 1916. Unfortunately, a lot of records were destroyed in the Four Courts during 1922, but for all papers related to Governmental Departments, et al.
They offer free Genealogical Services, which is great for people who don't know their way around the archives/ what exactly they're looking for. They've also put the Census of 1911 online, so now it can be accessed from anywhere in the world.
The archives are quite disorganised when you're actually in there and I've gone in several times and located files that I wanted to look at and the files were nowhere to be found. Also the archives don't have their catalogue digitised so you have to search through different finding aids to locate the files that are of use. They do have a bit of a search engine on their website, but it is limited in the results it returns/ the search criteria you can set. read more