To focus on the energies of wind, storm and the skies, the Wind Spire allows Monkey Apprentices to research and learn the most powerful Tempest Tornado spell.
”
~ BMC description
The Wind Spire is a Special Building in Bloons Monkey City. It allows the player to research the 4th tier upgrade, Tempest Tornado for the Monkey Apprentice. To build this, the player needs $15,000, 40 and can only be built on a mountain tile. It takes 36 hours to build. This building gives the player 500 experience points upon its completion. It requires Level 18 to unlock.