Hephaestus' cabin (#9) is for the children of Hephaestus, the god of blacksmiths and fire. The cabin is made of brick and has a smokestack sticking out of it, like a tiny factory or an oversized motor-home.
The entrance is like a vault door, circular, and of thick metal. It opens with a lot of gears turning and smoke hissing. It has shiny metal walls and metal slatted doors. It is noted for being unclean and messy, filled with junk often. There is a tunnel underneath it. There are only three Hephaestus demigods at the end of the war with the Titans because of Charles Beckendorf's death. In The Lost Hero, their numbers have risen to about a dozen boys and girls, although none of them look alike. The steel bunks were folded against the wall and had a digital control panel, blinking LED lights, glowing gems, and interlocking gears. A fire pole came down from the second floor and the cabin didn't appear to have a second floor from the outside. A circular staircase led down to the basement, power tools, an assortment of weapons, a workbench and a lot of scrap metal. Leo's bunk, Beckendorf's old bunk, has a built-in game station at the footboard, a stereo system in the headboard, a glass door refrigerator at the base, and a whole bunch of control panels running down the sides. The beds retract to a private room in the basement.
- Charles Beckendorf (former counselor, deceased)
- Jake Mason (former counselor, resigned)
- Leo Valdez (counselor)
- Nyssa (counselor, temporarily)
- Chameleon armor, forged by Charles Beckendorf.
- Festus, the giant automaton dragon.
- Their beds take them to underground private rooms.
- Leo's Magical Toolbelt, from which he can pull out regularly-used tools and food.
- Bunker 9 may count as it can only be opened by a fire user, such as Leo Valdez.
- Many other unnamed magical weapons (as the children of Hephaestus can forge almost anything).
- They are all expert builders.
- They are all mechanics.
- Technokinesis: As children of Hephaestus, they can control and manipulate machines.
- Can sense machines, mechanics, or metal.
- Can identify machinery type and use by touch.
- Can sense faults in metal ore.
- A few of them possess Pyrokinesis, a rare ability that Hephaestus blesses his children with every few hundred years, since the last demigod Hephastus blessed caused the Great Fire of London. The only living demigod with this ability is Leo Valdez.
- Can find and sense traps in the ground.
- Hephaestus' cabin has the most named inhabitants of all the cabins.
- They have the most counselors in The Heroes of Olympus.