I found this site completely by accident - it's at the north end of Copacabana Beach (to the left as you face the ocean from the beach). Cost to tour is about $2. There is an 800m trail (which is somewhat steep) through the restored rainforest to fort at the top. I saw several marmosets and lizards on the way, and the foliage was lush; I would guess it would be blooming had it not been winter. The view from the top is stunning - Copacabana beach on one side, Guanabara Bay and Sugarloaf mountain on the other, Redeemer statue in the distance. This is definitely worth the trip.
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