Originally Posted by
ZeroBG82
The first two areas you can access are Siofra River Well (found near the Mistwood in Limgrave) and the Ainsel River Well, found about midway up the eastern edge of Liurnia. Both are small areas where you will be able see sections you cannot reach.
To reach the additional section of Siofra, called Nokron, Eternal City, you will need to defeat General Radahn at the Radahn Festival at Castle Redmane in Caelid. This is the only way to access this area, currently.
From Nokron you can access an area called Deeproot Depths beneath the Capital. You can also get here via the Subterranean Shunning Grounds in the Capital sewers, so you aren't locked out of it if you don't beat Radahn. But, honestly, the Shunning Grounds are probably harder. Deeproot Depths has a path to Ainsel River Main, which is the part of Ainsel River you couldn't reach before. It also has a back way into the Capital if you come here first, and allows you to skip the boss guarding the Capitol entrance (though you have to beat like four other bosses to get here).
You can also access Ainsel River Main directly by doing the Ranni the Witch NPC questline. Which will first require accessing and completing Nokron, Eternal City. You will need to go through Ainsel River Main, and then through the Lake of Rot to the Grand Cloister and then further still in order to reach the final section of Liurnia, the Moonlight Altar, which is the plateau above the Village of the Albinaurics. There is no other way to reach this location.