Yes, the end of Blighttown is at the bottom of the mire. It takes a bit of exploring but the bonfire is not hard to miss and if you explore a bit more, you'll find both the boss of the area, as well as some cool items and secrets and even an easy way to farm Large Titanite Shards. The poison seems intimidating but it's not that bad; the damage tick down is not too agressive and it's best just to ignore it; after all, once you're poisoned you can't get further poisoned so just roll with it.Huh, I made it to the bottom and missed the bonfire. Climbed back out so that I could refresh estus.
I'm assuming the goal is down in the mire somewhere? I left as soon as I discovered the water was poison, despite seeing that there was an item available aways into it.