This is the easiest and safest way for a free walk into nature in Rio de Janeiro. I wouldn't miss it as a tourist. It's a one hour walk, about 30 minutes to go and 30 more to come back, 1250 meters at super easy level. With just a bit of luck, you will find monkeys and other small animals. It's in a military area, so it's extra safe for you to carry your camera. It's close to Sugarloaf and the excellent Urca bar, so keep in mind this combo. Air is fresh, the ocean is the view, and if you feel adventurous you can take a trail to Sugarloaf mountain from there. It's free, but be sure to get back before 6:00 PM, when the gate closes.
Praça Gen. Tibúrcio, S/N - Urca, Rio de Janeiro - RJ, 22290-270, Brazil