The Ruins were done for a test that got me my first 3d art job at Treyarch in 2001.  They provided a layout map with size dimensions, poly and texture limits, and gave me a week to complete it.  They let me come up with whatever theme and add whatever details I wanted so I made this little ruined temple with a tree growing in through the ceiling.  I painted all the textures by hand(with a tablet) and remember missing some sleep working on this up to the last minute.