Spiraling Skyline

When Spiraling Skyline enters the battlefield, sacrifice it unless you pay {g}, and return a land you control to your hand.
{t}: Add {g}{g} to your mana pool
{t}: You may play an additional land this turn. Spiraling Skyline doesn't untap during your next untap step. Activate this ability only once per turn.
When Spiraling Skyline leaves the battlefield, search your library for a forest, and
put it onto the battlefield tapped.