The 'mummy' was actually a 'mommy', as in the queen spider. Keep exploring the spider forest if you did not encounter her (in the north central area).
For the locked chest in the cave, did you notice that one of the walls surrounding it is an illusion that you can walk through? The walls around the key... <span class='standouttext'>Spoiler : </span><span class='spoiler'>are also partly illusion, and you can move the 2 barrels out of the way to get to the key.</span> (highlight the text to read)
After you complete the necromancer's task, you will be able to open the locked doors in the cave. Only the BF dungeons are randomly generated.
Note:
Complete all other quests before bringing the ingredients back to the alchemist and having him make the cure.
Lockpick is currently broke, and does not work.
