Underdark Caverns

Underdark Caverns enters the battlefield tapped.
({t}: Add {u} or {b})
{2}{u}{b}: {t}, Venture into the dungeon. (If you're
in a dungeon, advance to the next room. If you're not,
enter a new dungeon. Enter the first room or advance
to the next room)
Map in one hand, lantern in the other, they ventured
deeper into the mystical cavern.