Outside of Grand Temple
A Grand Temple is a large, mostly underground structure in the Overworld. It looks like a very big jungle temple, and extends ten levels under ground, all the levels look like large halls, with stairs leading down to the next, and each level has a different spawner, and a chest with increasingly better loot, for example: level one (above ground) has a giant rat spawner, or slime spawner, and in the chest are some cobble and some arrows, level two (underground) slime spawner, chest has three iron ingots and some cooked pork, level three has a sliver fish spawner and the chest has gold ingots and a wand, and so on, until you get to level 10, the deepest, and you get a a block of iron, and ten diamonds. In each Grand Temple, there is a Wall-phaser, that will hunt you from level 2-10.
Chests can be well hidden
The stairs to the next level
First level of Grand temple (Jack-o-lantern represents Spawner)