Yup. In fact I have a whole big tome devoted to the fortifications in Salvador da Bahia in Brazil.
I'd suggest looking at those for the following reasons:
Most are a manageable size.
Most are in very good states of preservation and reflect their 18th/ 19th C look (Forte Sant Antonio had a lighthouse structure added)
They pretty much all abut the sea or jut out into it.
Most date from the 17thC but took their current form in the 18th or early 19thC.
They tend to be relatively simple shapes but are none the less very attractive.
There are heaps of photos available on-line. Here's an example of a good example Forte Santa Maria. Spent a lot of time swimming in the adjoining cove, it's a popular beach and it's actually wedged between two forts.
https://whichmuseum.com/museum/forte-de-santa-maria-salvador-23064I'd suggest looking at the following ones in addition.
Forte de Nossa Senhora de Montserrat (my favourite) it's got a very elegant but simple hexagonal shape. really gorgeous setting too.
Forte de Santo Antônio da Barra. The grandest of the lot, the maritime museum is located inside. Absent the lighthouse, it's pretty much as it was in the 18thC. You'll probably get more results if you google Farol da Barra, as most people know it by the lighthouse.
Forte de São Diogo is an interesting example as it's an irregular hemipsherical shape. It was designed as the counterpart to Forte Santa Maria and overlooks it.
Salvador also has a fairly unusual circular fort set in the bay, Forte São Marcelo. The current annular shape dates to the 18thC.
Over on Itaparica Island, across the bay, you have Forte de São Lourenço. This one is beautiful and is more of the traditional star shape, you would see elsewhere. If you need further inspiration to research it in person, it's right near one of my favourite restaurants and the other best icecreamery in the state (the one at Montserrat is a quick bus ride to the best one in Ribeira). Our secret mind, few tourists visit that part of Itaparica.
There are a number of other forts set inland but these probably best meet your criteria. There are a heap more spread across Brazil, with concentrations in the South in Santa Catarina and also around Recife and Olinda. Rio has a large number of extant forts but most were remodelled in the late 19thC.
By the by, not a fort but a truly photogenic set of ruins of a fortified mansion, the Castelo de Garcia d'Ávila that dates back to the 16th C can be found a bit up the coast towards Praia do Forte. Might give you some further inspiration.
https://fgd.org.br/