If by that you mean upgrade, then you get a basement added to your home.
The basement doesn't do anything- it is an upgrade in your house that gives you more storage room.
Yes, It is the second to last upgrade you can get. The basement also comes with its own wall and floor, of which you can change at any time you wish.
its not secrete just upgrade your house alot and you'll get it
If you mean upgrade, (bigger room, basement, upper-floor) then for the animal crossing that I know of, you have to pay off your house. To do this you go to the post office and ask to "Deposit". It generally tells you how much you need to give until the next upgrade.
No. Unless you have a friend with a spare memory card or a animal crossing save already on it (meaning you wouldn't own the second).
You cannot upgrade your gate in animal crossing city folk.
The coffee shop is the basement of the museum.
No.
buy coffe from brewster in the basement of the mueseum
Nookington's is the last upgrade in the game and you cannot upgrade after you get it.
You will get a second floor and a basement.