I enjoyed Portal on the C64, so much so that I actually wrote Rob Swigart when I was toying with making a recreation of the virtual world it depicted. He though

I enjoyed Portal on the C64, so much so that I actually wrote Rob Swigart when I was toying with making a recreation of the virtual world it depicted. He thought it sounded like a fun project and even sent me a copy of the book. Probably should dust that idea off sometime.