Apparently firm believers that no ideas are bad ideas, the YouTube channel Play To DIY constructed a bicycle almost entirely out of concrete. The behemoth bike weighs an incredible 134.5 kg (~296 lb), and actually balances and rides pretty smoothly, all things considered. Those things to consider are it being made entirely out of concrete and weighing 296 lbs, just to be clear.
I like how it doesn’t have a brake. I feel like with the momentum you could gather on a 296 lb bike headed downhill, brakes might be important. I guess maybe that’s why they decided to construct a concrete bike helmet instead. Fight fire with fire! Or, in this case, concrete with concrete.
For reference, my street bike weighs 19 pounds, so this thing is almost 16 times heavier. Wow! And it’s already hard enough to get motivated to exercise on my bike; I can’t even imagine trying to convince myself to get on this thing. But you can rest assured it would 100% end with me easily talking myself out of it and taking a nap on the sofa instead.