The heart of any Spanish Colonial city is the central plaza, or Zócalo, and the ancient port town of Acapulco - despite its several modern facelifts - is no exception. The swirl of activity, the live music on weekends, the vendors selling every sort of cheap (and some very nice) souvenirs are all here, mixing and mingling with tourists and locals relaxing in the shade.
Like all central plazas, Acapulco's Zócalo is presided over by a Catholic church, in this case Nuestra Señora de la Soledad. Its unusually domed and stellar interior, bookended by two of the least traditional bell towers you'll find in Mexico, were originally part of a movie set, later redeveloped into a parish church and declared a cathedral (temporarily) in 1959. It is the perfect centerpiece to Acapulco's resort-chic collection of Mediterranean, modernist, and other original buildings.
Just behind the strip of high rise hotels fronting the main beach is the city itself, centered on Acapulco's Zócalo, more properly called Plaza Juan Álvarez. It is walking distance from anywhere in the city proper, and can be easily reached by Caleta or Base bus plying the Costera; taxis may be more convenient.
On holidays, religious or civic, this is the place to be, and you'll often find live music and dance, fireworks, and other festivities geared toward locals going on right here.