Cosmo's Den is a members-only land den that was formerly sold at the Diamond Shop.
On the inside, both floors have small cracks filled with flowing water. There are also built-in wooden shelves on the walls. There is a staircase made of leaves between floors. The wallpaper usually turns plant-themed. The flooring turns into carpets that are placed in various different sections of the den. There is a small stream flowing from upstairs to downstairs. Outside there is a big field.
- This den is featured in the Meet Cosmo adventure and appears to be part of a giant tree.
- The flooring is shown in rugs and mats that cover the ground, instead of one continuous floor. This is the first known den to have this feature.
- During the Denstravaganza event, it only cost 3 diamonds.
- The outside entrance is similar to the entrance to the Enchanted Hollow den.
- Although it is much bigger, it only has one entrance, unlike the one in the adventure.