I know an embarrassing amount about Silent Hill.
The winner, however, is Myst. I know how to count in D'ni numbers, I know where Ka'tran (punctuation?)/Catherine comes from, I know who she almost married instead, I know who writes which worlds with which style, I know why Gehn's worlds kept disintegrating, I know the names of the various ages even when we're not explicitly told, I know who the Grower is, I know what killed the D'ni civilization,
and I might know
a little bit
of Dn'i
language...
;_____;
If I had more time, I'd probably become an integral member of Myst Online, but as it is, I'm too busy to dedicate the hours and hours that other people do.