The only place to get a Brown Dragon Egg. The temple looks like a small brown pyramid with an entrance. Inside is a set of stair like blocks heading down to the main chamber where a small pyramid of obsidian is located, and a chest in the wall behind that.
Brown Temples are located in the Plains and Forest Biome.
The Egg is found at the bottom of the temple, encased in Obsidian. Break the obsidian and you get the egg.
The brown temple was the first temple to be added, and the obsidian challenge was added for a lack of a better idea.