well that depends on how you want to play, opening the door enables you to use a method that gives you 7k souls/3-5 minutes. behind the fog gate there's a boss that can be quite tricky for melee fighters, if you go as a human, you'll be able to summon a phantom that, to be fair, will pretty much do the entire fight for you. by the way, you should always keep your carryweight at least below 50% (I'm saying this because the elite knight set is heavier than whatever you were using before it).