The characters explored the mine. It was a maze of twisty passages, all alike.
After a few hours they came out into a cavern so large that their light sources could not reach the other side. They cast light on a crossbow bolt and shot it at the ceiling. There were bats. Lots of bats. They took objection to being woken up and swarmed the party.
After killing the bats and collecting and salting their meat, the party headed along the wall to the right and entered the first room they came across.
This turned out to be an old guardroom, wrecked by some explosion some time ago, with blast marks on the walls and chunks of the ceiling fallen down. There were also some skeletons, but Zai, the Cleric, made short work of them.
GM note: Nice to see the big abilities coming in to play.
A cold dinner and long rest in the guardroom, behind bolted doors. Nothing to burn, no sources of water.
The characters explored a coridoor and a room that turned out to be some barracks, inhabited by some ghouls and a ghast chewing on the remains of the long-dead defenders. The undead made good use of movement and opening and closing doors, but the party's ranged attacks were too much for them.
Something had been watching the fight from outside the room. It screamed in anger and flew up, into the rock roof.
Level 4! Feats! ASIs!
After a long rest, anyway.