Arguably humankind’s greatest engineering and technological accomplishment, the Apollo Program landed a human on a body other than planet Earth for the first time. Constructing and using the command and lunar modules was a major engineering feat. As per the Lunar Rendezvous method, the command module remained in orbit (with one occupant), and the lunar module went down and came back up (carrying two astronauts) – an elegant solution. Making the lunar module was a humongous challenge; it needed to be as lightweight as possible without compromising on any of its functions. In the end, NASA engineers ended up removing the seats themselves.
The construction of the Saturn V rocket is another impressive landmark. It burned 15 tons of fuel per second at lift-off, generated 7.5 million tons of thrust, and stood as tall as a third of the Empire State Building.
Personally, I find how NASA used archaic computer systems to process data and monitor the mission, doing everything from calculating trajectories and ensuring constant communication between Houston and the Eagle, pretty awesome. Do note that these computer systems, today, would be less powerful than an Apple Watch.
However, the most significant impact of the Apollo Program deviates hugely from the engineering and technological advancements it made. It showed Humankind an image of the Earth as seen from the Moon. Seeing this pale blue dot from afar, so small that it could be covered with the back of your thumb, had a profound, overbearing impact on people.
Concerning the future, I think the greatest feat of engineering in the next 100 years will be constructing a human colony on planet Mars. Doing so will require the development of means to transport thousands of tons of equipment, materials, and resources (along with humans) to Mars. We’ll need to set up basic infrastructure on Mars, and build habitats/shelters that enable humans to survive the harsh environment of the Red Planet; a thin atmosphere, dangerously high radiation levels, and wildly fluctuating temperatures.
Transporting materials and humans there will require space travel infrastructure. The sheer amount of traffic involved could warrant the construction of the first spaceport outside of planet Earth, on the Moon, from where taking off would be significantly easier due to a weaker gravitational pull. Reusable rockets will be key, so they must endure trips of upto 2 years upto ten times throughout their lifespans.
Providing water, food, and breathable air to future Martians will require technological innovation. Lab-based agriculture will not not be enough to feed an entire population, so alternate sources of food must be developed. Habitats would need to counter wildly fluctuating temperatures by cooling the system during the night, and heating the system during the day. Furthermore, setting up energy infrastructure on Mars will be even more hard. Solar is a viable option, but is rendered ineffective during dust storms. The current alternative, in my opinion, is nuclear fusion, given that the 100 years of progress that take us to a position where we can construct a colony on Mars also give us the means to harness the awesome power of nuclear fusion.