This impressive castle come fort in downtown Old Havana is also a very good maritime museum. For $3 CUC you can take a look around inside the castle with its super thick walls. Highlights for us were the model ships.
You cant miss this castle as you walk around Old Havana, its pretty impressive. Spend the $3 CUC and take a look inside, its very well preserved.
There are really nice views from the top looking out towards the two other forts on the opposite side of the harbour. The museum inside is also really good, unfortunately you arent allowed to take any photos, although we sneaked in a couple.
The model of the Santisima Trinidad ship built in 1750 and launched in Havana was amazing.