>The goddess gives you a pocket dimension
>She offers to put a city of your choice inside this pocket dimension
Ask to design my own city of adventure in the pocket dimension. Think Venice but sectioned into three tiers with the taller buildings forming interconnecting bridges/streets with each other, beneath the canals are underwater dungeons/sewers systems filled with monsters and treasure. Install myself as mayor with magical contructs as enforcers. Charge other adventurers a nominal fee to enter the city and dungeons respectively, all the normal fees for using facilities, and a percentage of the loot they acquire. Achieve immortality with the profits.
Somewhat lofty, but if the goddess tells me no I'm fine with just their blessing or something.