You need to go back to the depths where that "tiny little snouty monster is" From there, you'll get an item that lets you go further past the depths.
@Dangerous_Dan Thanks for the advice. Its a shame that New Londo Ruins might be too tough for me too. I'm a bit lost after that as I don't have any magic or pyro (I'm a big dumb Knight with lots of str, end, vit, and a bit of dex). I do have a wand though so maybe I'll go and experiment with that a bit. As for Blighttown - haven't come across it yet.
Have explored but not completed Catacombs, New Londo Ruins up to the bridge (not done much of it I gather), the Depths (found the little crocodile that turned into a big scary thing - when I first saw its snout we were like, "that isn't going to be too hard to kick in to shape" and when it fully emerged we were pissing ourselves laughing at our mistake), DR Basin (can easily sort out the knights and get to the butterfly but thats it), DR Forest (just opened the door with the Crest and nearly made it along the cliff edge to a building but then got mobbed). Still loving it though
Which is blighttown. Which is a nightmare when you first go there. Bear in mind there's 2 entrances to blighttown - the front door, which is via the depths after you kill the gaping gragon and get the blighttown key, and the back door, which is via the valley of the drakes (either go through the dr basin, or open the door from new londo (from firelink, go to new londo, come out of the initial tower, and turn right and go up the other tower - you'll need the master key to open this - starting gift, or sold later on by Domhnall (initially in the depths near the entrance to blighttown, and later on he's on the lower layer of the bridge that goes to the undead burg, right near the start at firelink)).
back entrance is useful when you want to razz through it, but it's probably better to do the front entrance first time around, as you'll miss some decent kit if you don't.
Take your time in blighttown, and wear as much poison res as you can. Take the spider shield from the depths with you to block the toxic dart blowing mother fuckers (that don't respawn, thank god). Also take the rusted ring from a return trip to the undead asylum - this lets you run at normal speed in the poisonous swamp at the bottom of blighttown.
There's 2 bonfires - 1 half way through and 1 at the bottom - be sure to be in human form at the bottom one, as it triggers an npc invasion that, once beat, you can summon for the quelaag boss fight.