We played D&D and took it very, very seriously. It got the point where we bought huge graph paper - like three feet by thee feet - and would spend weeks designing our own castles, which others would then attack. It was brutal.
Eventually we moved over to another game created by TSR called
Top Secret, which was very similar but set in the modern day. Players were secret agents fighting the cold war, driving fancy sports cars, etc etc. We created huge player characters and back stories, had pictures of our characters and their girlfriends....
We had so much with this stuff.
To this day I still have the original Top Secret game in it's box in my closet behind me.