Treasure Vaults are levels found only on randomized floors, alongside Graveyards. They contain few enemies, usually only a few scattered Kleptolisks, and are filled with an inordinate amount of Treasure boxes and Minerals. Treasure Vaults serve as a counterpoint to Graveyards, which are considered by some a "bad" floor to run into, and have the express purpose of rewarding any Knights fortunate enough to stumble upon them.
However, others would argue that Treasure Vaults are amongst the worst levels to run into; they give fewer crowns than many other levels, offer almost no heat, and even the numerous columns of minerals are worth little, since they are often of poor quality and few can be carried to the elvator. The main advantages they offer are an increased frequency of treasure box tokens, rarities, and their short length. Arguably, they still serve as a "counterpoint" to Graveyards, which contain more crowns than most levels if you kill all the zombies (but few treasure boxes).
Relax! Smell the flowers. Enjoy your day in the sun. You earned it!
Fortune Smiles on the Greedy
(Note: There are actually several minor variations of this level; they are all titled the same, however.)