lately ive been messing around with hammer which is the level editor for the hl2 source engine
spoiler (click to show/hide)
(http://xs137.xs.to/xs137/09126/wiphl2230.jpg)
its pretty fun to learn and I like looking at pictures of places for unique architecture and such things. right now I'm just kinda learning the basics then Ill probably do something serious with a layout in mind and probably whip up some custom textures in photoshop, which is also something I fuck around with from time to time. (though much more often)