The City hall sits on the Plaza de Armas next to Puerto Rico's version of the state department. The Alcalde dates from the 17th century with it taking its current shape in 1789. Numerous other historical and government buildings line the plaza.
Facing the Plaza de Armas is San Juan's City Hall called "Casa Alcaldia." Built in stages from 1602 to 1789, with symmetrical towers separated by arched colonnades, and an interior courtyard; Alcaldia's current architecture, which is the result of extensive renovations completed in 1841, is based on and was meant to be an exact copy of the City Hall in Madrid, Spain.
Also located within Alcaldia is an information center and art gallery space which hosts rotating exhibitions. It is possible that short tours can be scheduled by calling or stopping in Alcaldia, although apparently only certain spaces might be available for viewing. [We encountered a similar situation in Lima, Peru, at a beautiful city hall building -- although there were no tours available, we were invited to have a look around at the architecture and artwork in the common areas.]
Hours are 8 AM to 4 PM Monday through Friday.
While continuing your tour of Old San Juan, take a minute to notice what is underfoot.
Like the Capitolio, the San Juan City Hall is open to all visitors from Monday to Friday, 8:00 am to 5:00 pm. Located on the Plaza de Armas in a beautiful building dating back to the 17th century, the Alcadia frequently showcases small art exhibits that are accessible free of charge. Visitors can walk around the building on their own, which includes a really nice inner courtyard. Also, don't miss the back of the building (on calle San Francisco), it allows you to see the different types of architecture that were used in the design of the Alcadia.
As for the Plaza de Armas, although it was designed and is still described as San Juan's main plaza, it is fairly small and there isn't that much action going on (although we did enjoy watching two little girls feed the pigeons). There is a small fountain with four figures representing the four seasons, but it wasn't running when we were there. Also, it isn't necessarily surrounded by nice-looking buildings, the way most plazas are. The San Juan City Hall is by far the most interesting building in the area.