Sunken Citadel

Sunken Citadel enters tapped. As it enters, choose a color.
{T}: Add one mana of the chosen color.
{T}: Add two mana of the chosen color. Spend this mana only to activate abilities of land sources.

The Lost Caverns of Ixalan

Sunken Citadel enters the battlefield tapped. As it enters, choose a color.
{T}: Add one mana of the chosen color.
{T}: Add two mana of the chosen color. Spend this mana only to activate abilities of land sources.

The Lost Caverns of Ixalan Promos

"Land sources" include any objects with the card type land. This means you could spend the mana to activate an ability of a land you control or a land card in your hand or graveyard, for example.

You may spend the two mana added by the last ability on the same ability or on two different abilities.