The armoury is a part of the Kremlin but is an extra - entry isn't included within the Kremlin ticket.
Don't expect to see loads of armour in the armoury as the name is unrelated to its contents - I think the name comes from the tower of the kremlin wall its built next to.
It is reasonably interesting, there is armour and stuff but the exhibits are mainly ornaments, faberge eggs, clothes and royal carriages. No photographs are allowed in the armoury, with or without flash.
The audio guide is a must if you want to extract the most from your visit, and understand the contents of the display cases.
After your finished you can walk into the Kremlin, if you have a ticket.
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