Stalactites not only form from the ceiling of caves, but also from manmade structures like mines. Stalactites can be made up of minerals, lava, mud, or sand. The claim for the longest stalactite is 66 feet in a Brazilian cave.

FUN TIP: To tell the difference between stalagmites and stalactites, remember that stalagmites has a G for “ground” and stalactites has a C for “ceiling.”