You are not going to believe this. I am a 'dungeon master' of old! I played under another friend around '90 and then ran a game for one of my sons and his high school buddies. I ran some Dragonlance, Forgotten Realms, Undermountain, Ravenloft, Planescape and Spelljammer.
I used to write my own intros, fleshed out towns and cities, hopping from world to world. I was kind of generous over the years and they rose to mid twenties level in about 3 or 4 years of steady play. We had a real detailed world and characters, who even died once in a while! They played into their early college years. I still have a bookcase full of 2nd addition stuff!
Rex