What's One Home Upgrade That Was Worth Every Penny?

Now, I wonder to get an opinion from those who have finished the renovation. Can you name just one renovation that was totally worth every cent spent by you? You may refer to kitchen remodeling, bathroom remodeling, flooring replacement, energy-efficient windows, improved insulation or even installation of smart-home devices. Has the renovation positively impacted your everyday life or added some value to your home? Which of all these renovations can be called the best choice for you? If you have any recommendations for me, I would like to learn from your experience.