Favorite Game World.
I think that my favorite game world of all time was one that my best friend made. He designed it to be like playing Skyrim. Where you could be walking along and wander across quests or caves. It was a lot of fun the problem being that you could come across a quest designed for a level 12 party at level 1. It made it a very dangerous game as well but tons of fun.
In one instance we did do a quest at level 6 that was designed for a level 9 party. We were able to complete the quest, it was very difficult and made us think a lot harder about the risks. In the end we all made it out alive and with the people we were supposed to rescue.