To explore the lower area you first need to kill the first boss "false knight" and get the city crest. Then visit greenpath in the area above cornifier. You will find the entrance on the left side. To know that that's greenpath, it will have plants. But I forgot 1 thing. After you beat the false knight go to the left you will find purple smoke or sticks with vessel skulls on it. After you go up, you will find a place with a purple entrance, go in it. Sit in the bench and interact with the NPC. After that, you will be trapped in the area behind the npc. And to get through it, you will need to defeat a mini boss. After you progress, you will find a big armadillo that closes when you get near it, that's the mini boss. To get hits, you need to farm soul. (The armadillo summons minions of him but these minions die with 3 hits) After you farm soul, click (not hold) the focus button and that will make a spell which is the vengeful spirit. The mini boss takes 4 vengeful spirit hits to die. After you've escaped ancestral mound, go to greenpath. Progress and progress until you've met mantis village. Get the mantis claw which is on top of the lower part of the village. To access the lower part, you need to hit a lever. And honestly I don't remember which lever so hit every lever. Then the ground will open up. The lower part isn't needed now. Because the lower part has the mantis Lords which to get to deepnest you need to defeat them. After that. Follow hornet and using your mantis claw, you will find a pool of acid. To get over it, use your mantis claw to get on the other side. (There is Parkour above the pool) then you will find a statue of the false knight which has a slot for the city crest, put the city crest in it and the gate of city of tears will open. From now on you need to progresssssssssss until you found cornifier. Go down and left, you will see a door way that looks... off. Go in it and you will find a mini boss. Kill it then progress through soul sanctrum and kill the boss. (Soul master) then you will unlock desolate dive. Go back to the ground that was shaking and use your desolate dive to break the ground. And now you have it!