Katsunaya, the secret Citadel

Katsunaya, the secret Citadel enters the battlefield tapped.
Katsunaya, the secret Citadel doesn`t untap at your untap step.
Sacrifice 5 Lands you control: Untap Katsunaya, the secret Citadel. As Long as Katsunaya is untapped, you must not pay the mana cost of spells you control.