One of the servers i played at had a map with floating islands, with bridges connecting them, you had to unlock something to get to the next island, and every island had small quests.
I know it's a very vauge description, but it was probably the best time i had with minecraft. The server may not even exist right now, but if that's the case i want to look for something similar. I already tried the currently most popular servers at least 10 of them, but only found "vanilla" ones.
Any help would be greatly appreciated!