Like most tours in Brazil, you must speak portuguese to understand what's being said.. but if you're here, you probably speak the language anyway. If you don't want a guided tour, you can tell them you just want to take some photos and look around and you will be free to wander the fort and enjoy the scenery unabaited by the guide.
There are great photo ops. here from the top of the fort looking back towards Ponta Negra and Praia Do Meio.
You must park your car and walk a good distance to the fort itself. Where you park, there are some little open air flea market type shops where you can buy all kinds of shells and souveniers very cheap. I picked up a few huge shells.. one of which I found to STINK of dead fish returning to the states. OK if it's going in the garden.. but be careful when buying these - smell first! For less than 5$ US you can buy 3 medium size shells or one huge Conch shell - not too mention all kinds of other local handmade crafts.
Where you park there are usually kids hanging out - they will watch your car for you while you walk around and tour the fort for less than 1R$.

