Ah that one, yes i've been down there yesterday and picked up everything i could pick up. Several new locations are found that way, but i went back to finishing the other locations first. I made some nice progress today, really happy about it. Killed the Harvest Valley boss and also the Earthen Peak one. The feeling when you kill a boss, just so good. Sometimes summoning someone before a boss fight is very very tempting, but i did not do that for the those two and neither the two in Huntman's Copse.
Really cool fight. I went after those mages first and in the process hiding in those corners where you are save from the boss. After they were gone and the skeletons too, i had to find out how to really hit the boss because it moves so fast. I few times with the binoculars and magic, but what was absolutely sweet was that there's a lever. I used it. This closed the gate and the boss crashed into it...what was left to fight was the horsey. Great stuff.
I was curious how far along i was in the game and i searched for it online, turns out i have a shitload left, plus the DLC bosses.
http://darksouls2.wiki.fextralife.com/Game+Progress+Route
I am at 14 now.
I tried Iron Keep, but i kept being bothered by dark spirits and i barely hurt them, so that was definitely a sign that i shouldn't be there.