Vaults are featured throughout the Fallout series and are generally inhabited by dwellers whose ancestors were lucky enough to enter a vault before the bombs fell. Vault-Tec was in charge of the vaults, and they proceeded to conduct some questionable experiments on the residents. These experiments ranged from opening a vault a certain amount of time after the Great War to pumping drugs through the vault's air system, drugging the inhabitants.
A few vaults found throughout the series did not have experiments and were instead actually being used to preserve the human race. While a lot of the vaults found throughout the series are known, there might be a few vaults fans have missed.
10 Vault 77
Vault 77 was first shown in the comic One Man, and a Crate of Puppets, which follows the adventures of a lone vault dweller. The experiment for this vault had the man locked inside a vault alone with only a crate of puppets for company. This most likely caused him to go insane.
The vault dweller's jumpsuit can be found in Paradise Falls in Fallout 3, along with a holotape from worried slavers. The slavers are worried the dweller will be back for it, suggesting the jumpsuit should be burned. The vault suit will also give the player a boost to unarmed and melee skills.
9 Among The Stars Vault
The "Among the Stars" vault can be found in the Galactic Zone of Nuka-World in Fallout 4. The vault shows what a vault on another planet would look like, while also experimenting on the attraction's visitors. The tests included brainwave disruption, subliminal suggestions, releasing an airborne toxin, and releasing a small amount of radiation into the attraction.
A fifth test was performed, combining the other 4 experiments and performing them on the staff. Players who explore the vault will be able to see a unique take on what Vault-Tec's iteration of a space colony would look like.
8 Vault 43
Vault 43 was also shown in the One Man, and a Crate of Puppets comic, only being shown in the introduction. Not too much is known about the vault, except the fact that twenty men, twenty women, and a panther were locked in the vault together. Fans of the Fallout series can probably assume what happened with this "experiment."
Assuming this vault looked like the others, the dwellers could have potentially managed to lock the panther in a room. That being said, maybe all of the dwellers were killed by the panther, ending the experiment early (or on time, depending on how you look at it).
7 Vault 69
Vault 69 was another vault mentioned in the One Man, and a Crate of Puppets comic, with the experiment locking one man in a vault full of 999 women. There was a counterpart vault mentioned in the Fallout Bible and cut content from Fallout 2 which reversed the roles.
While not much is known about this vault, it most likely was an experiment to see what would happen if there was only one mate capable of breeding with the rest available in the vault. Needless to say, it seems like a recipe for disaster.
6 Demonstration Vault
The Demonstration Vault was found underneath the Cathedral in Los Angeles and is the base of The Master. This vault appears in the first Fallout game, being the first vault that Vault-Tec built. Despite being a demonstration vault, people still hid in it during the Great War and survived.
This vault can be destroyed when the player is tasked with killing The Master. By using a nuclear bomb, the vault is destroyed and the inhabits are killed off, ending the Super Mutant threat.
5 VTU Simulation Vault
While not technically a vault for survival, this was used to train overseers and vault technicians at Vault-Tec University. While the vault was sealed during a test, the Great War occurred. Other issues in this vault include a paste that tasted horrible and black-market food that caused health issues.
Players who venture into this vault can see the skeletons of the students who were trying to get out. The skeletons have a unique VT jumpsuit, which can be found at the university. Sadly, it would seem this overseer did not pass his test.
4 Vault 88
Vault 88 is found in the Vault-Tec Workshop DLC for Fallout 4. This vault is unique, as it was never complete and the player is able to build onto it. This means the player can make a vault that looks completely different from others found in the wastelands.
The player can also enlarge the areas they can build by clearing out rubble and killing off enemy creatures found in the vault's caves. After this is done, dwellers can be recruited and the vault can finally be inhabited.
3 Unfinished Vault
The Unfinished Vault is found in Fallout 2, showing the caves of where the vault would go. Had the Great War not occurred, this vault would've been finished and Vault-Tec likely would have gone on to build many more. It is noted it also looks similar to how Vault 13 looks.
Players can discover this location by buying a Holodisk from Merk for $1000 while looking for Vault 13. After finding the caves, players can go back and get their revenge for being scammed.
2 Vault 11
Vault 11 is found in the Mojave Wasteland in Fallout New Vegas. The experiment associated with this vault is that the inhabitants would need to vote for someone to sacrifice themselves, or everyone in the vault would die. The dwellers go along with this macabre process until they decide they have had enough.
The dwellers that are left decide not to sacrifice anyone, being surprised when they are congratulated on selflessness. It is revealed the whole point was to not sacrifice anyone, making those deaths pointless. The leftover dwellers don't know what to do and are wracked with guilt, so they commit suicide at the vault's entrance.
1 Vault 17
Vault 17 has not been seen in a game yet, but is mentioned by the companion Lily Bowen in Fallout New Vegas. Lily lived there with her grandkids until she was kidnapped by The Master's army, turning her into a nightkin. It could be assumed the vault was destroyed during this invasion.
Interestingly, a Vault 17 jumpsuit was supposed to make an appearance in Fallout 4. Maybe the vault's location was going to be retconned, or Bethesda forgot the number 17 was already used for a vault.