Apocalypse is a term that has been used for ages and so people have done different things to prepare themselves for those bad days. Your grandfather was no exception. He was a rich man and so he spent a huge amount of money to construct an underground fortress but it was never used because the apocalypse never came. You were informed about the fortress just before your grandfather passed away. So, now that you are the owner of the property, you decide to go an inspect it. After you have gone through all the different areas inside the fortress, you decide to leave for home but you just cannot find the exit. Yes, you are trapped. Self help is the only help you can expect in a secluded place like this.