Many of us have probably had the same idle thought at times when driving over a massive structure like the Golden Gate Bridge: 'How the heck did they build that?'
Things get particularly tricky to wrap your head around when you think about how much of the construction is underwater.
Thankfully, a helpful new YouTube video from the channel Lesics is expressly designed to explain this civil engineering challenge.
It does this nicely and simply, making it easy to understand, starting way before construction at the point when the ocean or river bed is tested for soil density and consistency - to work out if building something is even possible.
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Typically engineers build a sort of temporary dam in the river, a wall in the shape of a loop around where the construction needs to happen - this can then allow them to pump all the water out of the section.
As the animation makes clear, though, this dam needs to be very carefully reinforced to avoid collapsing inward - these bracing frames look like literal life savers.
All of this basically means that you have a gap in the water where you can work on your construction without needing a diving suit or submarine. Even then, water will often seep in at the bottom, through the ground, so constant pumping is needed.
The video explains that a concrete bed poured in can help stop this seepage, and also be part of the foundation-building process - so it's doubly useful.
With foundation piles in this concrete hammered into the bedrock and reinforced, you're left with a really solid foundation on which to build upward to create your bridge's leg or whatever else you might be planning.
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Still, from this point onward there are likely to be plenty of workers down in this slightly creepy dammed hole in the water, building and reinforcing things according to the design - that is an undeniably scary place to work.
There are, of course, other techniques that crews can choose to build underwater structures, but this process is particularly suited to bridges.
In an era when we're perfectly capable of sending probes to Mars and missions to the Moon, it's always surprising to learn how complicated it can be to build things back here on Earth.