Catacomb of Bones

It's been two days since you fled down under the city. Ten days since the sky turned dark and the rains started. The news called it an acid rain but the truth is that it's far more potent than that. A few drops will cause flesh to melt from bone. We sheltered inside our houses at first, but as critical infrastructure began to fail, the situation became even more untenable. Power lines were severed, causing widespread power outages, and even some isolated fires. Roofing shingles even didn't stand a chance, nor did many of our timber-framed houses. Things began to collapse within days.
Worse, five days ago they appeared. Clawing at the doors of the more sturdy buildings, breaking in and slaughtering the inhabitants. You thought about trying to make it to somewhere more sturdy. One of the abandoned castles, maybe. But there was no way past the rains - they would have eaten through you in a minute. So you and your fellows who had been hiding out in the old University, took down to the tunnels - the entrance had been blocked off for a long time, but it was still down, at the depths of the library's basement. You knew the way.
You found yourself in ancient catacombs. You'd known that there were centuries of bodies buried here, but you weren't prepared for the sheer amount of bones you would encounter. The walls, columns, everything. Covered in bones. Ornate. Decorative. Bones.
They were behind you. You had to flee, deeper into the tunnels. Taking what light you could with you and hoping it'd hold out. What you found was nothing short of miraculous, and horrifying. A necropolis, underground, vast and wondrous. You have no idea how it came to be here or why the acid rain is being funneled into vast cisterns around the city - but you have nothing left to lose, maybe it contains something you can use to fight them off, or find some other exit from this nightmare.
Areas of Note: The Bone Tunnels, Acidic Cistern, The Canals, Lichmoss Storage, Vast Tombs
Goal: Explore the Necropolis, avoid or fight them, and try to secure an escape route.