Skyscrapers. They might seem like a smart, efficient way to increase urban density by fitting a lot of condos or offices into a relatively small area of real estate.

They have great views, and attract tourists.

They are feats of engineering (think foundation, vibration and wind) and are sometimes beautiful works of architecture (see No. 29 on this list.)

They take their share of criticisms. They are often said to represent certain body parts. Critics say they create massive shadows, wind tunnels, alter iconic skylines, cost too much, provide little benefit to the local population in terms of solving issues like housing shortages, and they use a lot of cement, which is responsible for about 8% of global CO2 emissions. Their aesthetics are often reduced to the mundane (Shanghai’s World Financial Center — No. 11 on this list—is likened to a bottle opener.)

Many skyscrapers are actually mostly empty near the top, (29% of Burj Khalifa, the tallest in the world, is non-occupiable) and some stand unfinished or even abandoned, like North Korea’s Ryugyong Hotel.

Whether or not people return to working in offices after the pandemic could have an impact on these spires of the commercial real estate industry. But we’ve said this before, after the attacks on the World Trade Center in 2001, when it was debated that people may no longer want to occupy these potential targets of terrorism, these swaying, wind-buffeted towers that require a great deal of security and that some fear are also vulnerable to earthquakes, fire and collapse.

These are the tallest completed buildings in the world, according to the Skyscraper Center.