Imagine that you regain consciousness and find you're in a phone booth completely encased in concrete. Imagine that all you have with you are the contents of your pockets and a few mysterious documents. Imagine that you have only 48 hours to live, unless you can find a way out.
Or better yet, don't bother imagining it. Just read (if you haven't already) Jason Shiga's amazing Fleep. And while you're there, check out Shiga's other work - including the marvellous Bus Stop. Easily some of my favourite web comics.