One of the things I geek out over in games is maps. I used to make maps for a game with a colleague of mine, although unfortunately we grew distant and it never completed. Some other things I love are bestiaries like in Final Fantasy 12, item compendiums like in Star Ocean Till The End of Time, Maps like in Oblivion, massive amounts of clutter like in Elder Scrolls games.....hmm I can go on forever  It all seems to be side things hahaha.