Indonesia, Thailand, & Myanmar
While the mangosteen will never replace the mango (no relation) as the most supreme tropical fruit, most people agree it's right up there as one of the most delicious and delightful fruits.
Its hard and fibrous purple rind protects a white fruit that is tangy sweet. The fruit sections inside have a texture similar to but softer and spongier than citrus.
Once mangosteens are picked ripe, they spoil pretty quickly, so it's hard to find mangosteens anywhere outside of the tropics. The New York Times reported in 2007 that the purple fruits were available in NYC for about $45 per pound. At prices like that, I'd suggest you just hop a plane to the tropics during the mangosteen season.