While most ancient wonders were built upward, this one was carved downward, straight into the earth.
Takht-e Rostam, near Haibak in northern Afghanistan, is a Buddhist stupa monastery from the 3rd to 4th century AD. Instead of stacking bricks, ancient engineers excavated a massive circular trench around eight meters deep into a solid limestone hilltop, leaving a single core of untouched rock to be sculpted into a stupa.
Around it, five chambers were hollowed directly from the bedrock, two of them sanctuaries, one with a domed ceiling carved into an elaborate lotus pattern.
They didn't build a monastery. They subtracted one from a mountain.