Michel Reuge's Vault is a hidden chamber under London built inside an old bank vault. Collect all the discs from the Secrets of London music boxes and it opens, giving Evie the Aegis outfit once worn by Minerva.
The Swiss Assassin Michel Reuge found the Aegis, an Isu suit of armour, near Bath. It nearly drove him mad, so he locked it away and scattered the keys around London in music boxes.
A year after the twins open it, they are drawn back by Alice, a former teammate of Reuge's who joined the Templars out of obsession with the Aegis, and confront her inside.
Inside, Evie fits the discs into Reuge's device, and the armour is revealed behind it. Hunting the music boxes is a citywide collectible chase, so it pays to look out for them as you clear each borough rather than leaving them all to the end.
Bed and Bottle
The Bed and Bottle is a pub and lodging house in the Strand run by the Templars Argus and Rose Bartlett, who use it to make guests disappear. Their Templar Hunt brings you here.
College Wharf
College Wharf is a Southwark loading dock on the Thames. You go there for Alexander Graham Bell in Cable News, freeing his crew and recovering seized cable reels, and later return to help set an ambush on Templar dynamite smugglers.
Owers Manor
Owers Manor is Lady Owers' country house in the Cotswolds, northwest of London. In The Lady Talks, Evie travels there to assassinate her as Jack the Ripper's lieutenant.
Sinopean Club
The Sinopean Club is a gentlemen's club for Disraeli, Gladstone and the Earl of Cardigan. Jacob infiltrates it in Playing Politics to learn who "B" is, and in Family Politics Evie drives Gladstone there in a stolen royal carriage.