You can find it in local markets, or watch it bend the branches of the plant on which it grows, the Annona muricata.
It may seem harsh with its spines and huge (a single fruit can weigh up to 2 kg), but not only is it edible, but it is one of the most beneficial fruits found in nature. 
We are talking about graviola, also known as Corossole or Guanàbana, very common at the equator. 
Its bright green skin (it becomes a little duller and darker when ripe) is thin and has non-hazardous spines. 
The flesh is soft, generally white in colour and has a fleshy, juicy texture and a slightly acidic but very sweet taste, the fruit has many black seeds inside that can be easily removed.
It can be cut in half and enjoyed directly with a teaspoon, or used for the preparation of smoothies.
In Kenya, where it abounds, they call it "dawa tamu", which means "sweet medicine". 
The graviola is a low-calorie fruit, rich of vitamins of the group B and C, iron, magnesium, potassium, proteins and amino acids. 
To these are added other elements with particularly therapeutic indications: acetogenins with anti-tumor qualities, Y-amino butyric acid (GABA) for anxiety, coumarins against bacteria and much more. Precisely for these qualities, the fruit - but also the plant and the leaves, where these elements are more evident - has been utilized since centuries as a natural remedy for the treatment of the most common pathologies, from the infections to the high blood pressure (the assumption of the fruit leads to a natural decrease of the blood pressure, therefore the recourse can be indicated for those suffering from hypertension).
The assumption of graviola is also recommended for the treatment of intestinal worms, in case of stress and nervous problems, for eliminating lice, as well as for toning and strengthening the heart.