I grew up in a town of 45,000 in central, New Jersey, (Plainfield), and there was a sizeable shopping district that we always referred to as downtown... Goin' downtown? Let's go downtown... etc.

"When you're alone/and life is making you lonely/ you can always go....downtown"
--Petula Clark

In New York City, however, (where I spent a lot of time as a kid, and then lived for awhile) there is a very definite uptown. (I'm surprised you missed this Helen). There are two posh areas adjacent to Central Park roughly from (streetwise) the 60's to the 90's called The Upper East Side and The Upper West Side (where John Lennon lived in the Dakota).

Uptown Girl/she's been livin' in her uptown world....And now she's looking for a downtown man/That's what I am....She's getting tired of her high class toys/And all her presents from her uptown boys.
--Billy Joel

However, the classic Uptown is north of 125th Street, Harlem, as in the flick Uptown Saturday Night

Atlantic City is built on the northern portion of a barrier island, Absecon Island, but the communities south of the city on the same island, Ventnor, Margate, and Longport, are referred to as downbeach. However, Atlantic City is never referred to as upbeach, the term just doesn't exist. Folks there just say "go into town" or "go into the city" or "go to Atlantic City."

foreshore

Intriguing, CapK...never heard that term on the East Coast of the US anywhere (from new England to the Florida Keys, and Gulf Coast). Does anybody use this term anywhere other than "Upunder" ?