Hammer is an unlivable alternate universe. It is unlivable due to its lack of biological material. It is made primarily of cold, rocky planets most of which are rogue.
Hammer is used for Hammerspace. It is where most of the hammerplaces are. Hammerplaces are the storage cellars. Technically, hammerspace is also the storage cellars, but more often refers to the entire concept.
There is a lot of real estate in Hammer, so Space Travel must be used.
Hammer is known for being scary, and giving people chills because of its bareness. There are a mere 7 known stars, all in very close proximity to each other; it is pitch black there, and there are no sprinkles of stars in the distance.