The crags are a biome consisting of cobblestone, stone and Overgrown Stone. They can get up to as high as the world sky limit, so if you aren't careful you may fall and if you do, you'll most likely die. Some places in the crags would be brilliant places to build grand fortresses. Underground, you can find Emeralds. Water used to be coloured dark dull blue until 1.11.2 where the biome was redesigned. Crag Rock has been removed too.
Surviving in the crags can be difficult since only Damp Grass grows here. Your only food source would be rotten flesh and rarely carrots and potatoes from zombies and your only source of wood occurring in this biome would be from the lucky find of an abandoned mineshaft. Other things such as seeds, saplings and passive mobs would have to be transported here. It's not the best biome to start off in because of these factors.