Some outer planes
by Marco DalmonteOne (Yzorderrex) was basically a huge city completely surrounded by the Vortex except for the gateway to the astral plane (constantly guarded by a monolith-like baak). The whole city is miles long and wide, and near the end (judging from the entrance) lies a majestic tower (1 km high) that can be seen from any point of the city (provided you're high enough). There are various creatures living in the different quarters of the city (called kesparate), each one with its customs and diets and all of them interact living their day off like in a normal prime plane metropolis. only in this case they produce everything they need to survive inside the various parts of the city, and they must trade with one another to get what's needed. A special police force composed by titanic beings that slowly move across the wider streets patrol the city. When something's wrong, one of them pops up and solves the matter with rude violence. If troubles arise, they have a collective mind, so they all know what's happening and who are the criminals... etc..
Another one (Jokalaylau) was a flat world with one great ocean limiting the land to the south west and a huge mountain chain to the northeast. The hundred miles wide plains that lie between these two geographical features are sparsely inhabited by birdlike people who have got a matriarchal society and have enslaved males long ago. they consider all kind of males inferior and if any male circulates in their cities, they have to be chained and owned by a female mistress, else they're seized and put in the common pits with other males without master. The fate of these males is to be used for reproduction or as meat to sell in the realm or in the astral plane. It is said another realm ruled by the males exists in a fiery desert behind the mountains, but nobody has ever seen it and nobody dares challenge the holy mountains to find out the truth...
Another one I detailed is Terra's
homeplane, basically a gigantic sphere of rock and stones where
tribes of different races live peacefully alongside. They are
nevertheless always huge by human standards and eat strange rocky
substances to live on. There are oracles of Terra in every part of
this gargantuan planet, usually built atop the highest peaks (10
miles high!) and it's a heck of a trip to arrive there, especially
for those who cannot fly..