The vault is at the centre of the 10 Years of Minecraft map, and is the route to reach most of the other main areas of the map.
After taking a looooong minecart ride through the history of Minecraft you will reach the door to the vault. There is a chest on the right with a book in it with some information about the vault and a map. In front of you is a solid stone wall, and the area behind is blocked by panes of glass. On the walls on both sides are signs with the numbers 0-9 on them and a wooden button under each one.
The book has a couple of pages of writing but the thing to notice here is that it says at the top that there are 12 pages. Keep going through the blank pages and 10, 11 and 12 you will find the code:
17 05 09
This is the date (in European format) that Minecraft was first released!
Press the button under each of the correct numbers in order and the stone blocking the entrance to the vault, and the glass blocking the route to the mob gardens will disappear!
If you need any more help navigating the 10 Years of Minecraft map, take a look at our guide to getting into the Academy.