I guess you could put it on ever higher stilts to satisfy the parallel and level thing.

We do have examples of buildings needing to account for the curvature of the earth.

One that comes to mind is The fountain at the Christian Science Mother Church in Boston…

It’s about a quarter mile long and the water flows evenly over the granite curbs along its entire perimeter. If it didn’t follow the earth’s curvature the water would all just spill over at the middle.

Im very surprised that noone here has mentioned the LHC in CERN Headquarters, Geneva, Switzerland. The LHC or Large Hadron Collider is so huge that it stretches across 2 countries (France and Switzerland) and stretches over a circumference of an impressive 17 miles (27 kilometers). It is so large that when building it they not only had to take into consideration the curvature of the LHC tunnel, but also the curvature of the earth as the question asks. Very Big.

As a pediatric but fun point, in surveying, level lines are defined to follow the Earth’s curvatur. This means they are technically not straight. Horizonal lines, which are perpendicular to plumb lines, are often used as approximations for level lines.

Generally it’s safe to use them interchangeably, but sometimes the distinction is important.

theconstructor.org/surveying/…/20077/?amp=1

Relatedly, some long structures that seek entirely straight have different lengths depending on the altitude you measure them. For example, an oft repeated tidbit is that the Lake Ponchartrain causeway is two inches longer when measured at the deck than at water level due to the earths curvature.

I can do it. Two walls: one on the north pole and one at the south pole would be parallel and plumb.